Good FOSS applications -- user facing software -- are collected below. Please make sure any software you add has at least a basic development and user community.
- Orca - screen reader and voice access.
- SITPLUS - eye tracking.
- Viacam - mouse replacement.
- Vinix - Ubuntu optimized for visually impaired users.
- jGnash - personal.
- GnuCash - personal financial management.
- LedgerSMB - SQL-Ledger fork.
- SQL-Ledger - first professional and now leading FOSS accounting app for businesses.
- KTooN - 2D animation.
 Association / Non-Profit Management
- CiviCRM - first and now standard FOSS app for association management, events, campaigns.
 Artificial Intelligence (AI)
- AliceBot - natural language chat bot.
- co.py.cat - python implementation of Douglas Hofstadter's copycat algorithm.
- Deeplearning4j - Java implementation including
- Mahout - Apache project for scalable machine learning.
- OpenCog - concerned with generic intelligence and the inter-related cognitive processes it entails.
- Torch - machine learning framework with linear algebra, neural network, and energy-based model support, and packages for audio, computer vision, images, networking, signal processing, video, and others.
- Arduino Telescope ASCOM Driver - hardware controller standard.
- AIPS - Astronomical Image Processing System.
- GNU Radio - for radio astronomy.
- INDI - distributed control protocol for astronomical instrumentation.
- JSkyCalc - time and sky calculations.
- Observation Manager - astronomical observations logbook.
- PHD Guiding - intelligent auto-guiding.
- SGL Observatory Automation - automate an astronomical observatory.
- XEphem - sky charting.
- XmTel - telescope control software.
 Audio Editing
- Jack - audio connection.
- Ardour - digital audio workstation.
- FreeDownloadManager - multiple download methods.
- Time4Popcorn - Popcorn Github - movie streaming.
- qBittorrent - bittorrent client.
 Business Intelligence
- Pentaho - one of the first FOSS BI systems.
 CD/DVD Creation
 Church Management
- ChurchDB - management of families, integration with Google Maps.
- Asterisk - first and now standard Voice over IP (VoIP) management system.
- Ekiga - conferencing support.
 Computer Aided Design (CAD)
- BRL-CAD - solid modeling, interactive geometry editing, high-performance ray-tracing for rendering and geometric analysis, image and signal-processing.
- LibreCAD - standard open source CAD app, works with BRL-CAD.
Also see 3D modelling app "Blender" in Graphics section.
 Crowd Sourcing
- Ushahidi - dispersed information collection and mapping.
 Customer Relationship Management
- OpenCRX - with ticketing and issue management.
- vtiger - standard FOSS fork of original SugarCRM software.
- GNOME - most widely used Linux user interface, underlying Ubuntu.
- KDE - second most widely used Linux user interface.
 Desktop Publishing
- SCRIBUS - standard FOSS app for magazines, bulletins, handouts, posters.
 Development Environments
- Code::Blocks - Cross platform C, C++ and Fortran IDE, extensible, and configurable.
- Eclipse - standard FOSS integrated development environment (IDE), foundation supported by almost every major tech company, based in Ottawa, Canada.
- Lazarus - Delphi compatible cross-platform IDE with components ready for reuse, and a form designer to easily create complex GUI's and apps.
- MonoDevelop - Cross-platform support for quick development and porting of Microsoft C# and other .NET applications for Linux, Windows and Mac OS.
- Qt - Cross-platform application and UI framework for C++ and QML.
- SharpDevelop - Open source IDE for C#, VB.NET and Boo projects on Microsoft's .NET platform.
 Disaster Management
- OpenRelief - inexpensive drone controller.
- Tickets CAD - dispatch management and tracking system.
 Document Management
- Alfresco - one of the first and most widely used doc management systems, several commercial open source components but makes the list because they converted back to the GPL License.
- Nuxeo - standard FOSS doc management system from Europe, all FOSS components, scales from small to very large organizations..
 Ebook Readers
- Drupal Commerce - for Drupal websites.
- nopCommerce - asp.net based cart.
- Open For Business - one of the first FOSS e-commerce systems.
- oscommerce - one of the first FOSS e-commerce systems.
- RapidShop - shopping carts.
- Ubercart - integrates with Drupal.
- Virtuemart - integrates with Joomla.
- Course Builder - by Google.
- Moodle - one of the first and now most widely used FOSS education apps.
- VUE - unique capabilites, extraordinary visual mapping tool to help organize digital resources.
 Email & Calendar
- Evolution - widely deployed world wide by Novell in late 1990's, the standard enterprise level client.
- Thunderbird-Lightening - Mozilla (Firefox) supported client, most widely used individual FOSS client.
 Email Marketing
- OpenEMM - emails and campaigns with automated opt-out compliance.
 Emergency Services
- Open ISES Tickets - Information Systems for Emergency Services (ISES).
- Code-Aster - Civil and Structural Engineering finite element analysis and numeric simulation in structural mechanics.
- Adempiere - one of the very first FOSS ERP solutions.
- OpenERP - one of the most widely used.
- opentaps - one of the most widely used.
 File Compression
- 7-zip - support for gzip, zip, related formats.
 Flight Simulator
- Blender3D - 3D modeling.
- Cenon - vector graphics.
- DIA - first FOSS template tool, occasionally useful, now superseded by LibreOffice Draw, Gimp, Inkscape, and others.
- Gifsicle - create animated gifs.
- Gimp - standard FOSS bitmap editing application, extraordinarily powerful.
- ImageMajick - create animated gifs.
- Krita - painting and sketching.
- Inkscape - standard FOSS vector graphics application.
- Diagram Designer - Simple vector graphics editor for creating flowcharts, UML class diagrams, illustrations and slide shows.
- Graphite - scalable real-time graphing.
 Groupware (email, contacts, calendar, notes, tasks )
- eGroupWare - web-based.
- Group-Office - web-based
 Health / Medical / Dental
- Eclipse OHF - health framework.
- GnuMED - electronic medical records.
- OpenDental - dental application.
- OpenEHR - electronic health records.
- Open EMR - electronic medical records.
- OpenMolar - dental software.
- OpenTox - interoperable predictive toxicology framework.
- OSCAR - electronic medical records.
- VistA - electronic medical records.
 Human Resources (HR)
- OrangeHRM - first FOSS HR management software.
 Instant Messaging
- Pidgin - standard FOSS app for IM, can connect to all major networks.
- PHIRC (IRC)
 Inventory Management
 ISP Management
- Freeside - billing, CRM, trouble ticketing, network monitoring and provisioning for ISPs, VoIP providers and other industries.
 Issue Tracking
- Trac - standard (basic) FOSS issue tracking app, simple interface, customizable reports.
(See "Bug Tracking" software on "System Software" page for more sophisticated systems.)
 Label Printing
 Library Software
- Mathbuntu - learning software.
 Mind Mapping
- ArgoUML - UML modeling.
- Modelio - UML, BPMN, Java, XMI, HTML, Jython modeling environment.
- UMLet - text-based UML modeling.
- HandBrake - format conversions.
- Hugin - panorama photo stitcher.
- WhisperNote - portable encrypted HTML note.
 Office Suite
- Calligra Suite - Koffice spinoff.
- LibreOffice - standard FOSS office suite software, compatible with Microsoft Office, update of original OpenOffice.org.
 Optical Character Recognition (OCR)
- JavaOCR - suite of "pure" Java libraries with no external dependencies, small memory footprint, good for Android development. (Apache 2.0)
- ocropus - Python-based OCR package using recurrent neural networks, including scripts for ground truth editing and correction, measuring error rates, determining confusion matrices, and other features. (Apache 2.0)
- OpenKM - enterprise focus with modules such as version control, metadata, workflow, search, and user collaboration. (GPL 2)
- Tesseract - very accurate, works with Leptonica Image Processing Library in 60+ languages, developed by HP, now led by Google. (Apache 2.0)
 Password Managers
- EveryPass - a HTML5 based password manager that allows cross domain password management on modern, web enabled devices.
- KeePass - open source, light-weight and easy-to-use password manager for Windows, Linux, Mac OS X and mobile devices.
 PDF Viewers / Editors / Writers
- CC PDF converter - PDF printer.
- PDFCreator - PDF printer.
- Hugin - panoramic photo stitcher togetherer.
 Point of Sale
- Sozi - zooming presentation editor and player.
 Printing 3D
 Project Management
- GanttProject - Gantt charts, reads/writes MS project.
- Planner - simple interface, Gantt charts, resource allocation, cost roll-ups, HTML export, best basic tool.
- ProjectLibre - update of original OpenProj app, Gantt charts, resources, costing, read /write compatible with MS Project, best sophisticated tool.
- RedMine - web-based collaboration support for project teams.
 Real Estate
 Reporting / Charts / Graphs
 Resource Management
- Kazam - screen recording for screencasts.
 Search Engine
 Social Networking
- Diaspora - modeled on Facebook.
 Sound Editing
 Survey Software
 Terminal Emulation
- PuTTY - Telnet, SSH, xterm emulator.
 Timesheet & Time Tracking
- Timesheet Next Gen - spin-off of long-time Timesheet.php.
- Lyx - LaTeX based beautiful typesetting editor.
- TeXmacs - LaTeX based beautiful typesetting editor.
 Video Capture
 Video Players
 Video Conferencing
 Video Editing
- Avidemux - good video conversion, rotation tools.
 Virtual Desktop Clients
 Virtual Private Network
 Virtual World / Simulator
- Gaze Tracker - gaze tracker.
- OpenCV - computer vision libraries.
 Voice Calling
 Voice Recognition
 Website Analytics
- Analog - started in 1995, still being enhanced.
- AWStats - started 2000, command line tool.
- Piwik - includes marketing and related analysis.
- Webalizer - fast C code, HTML reports.
- W3Perl - all Perl, email and HTML and PDF reports.
 Web Browser
- Firefox - standard FOSS app until Chrome took more user share, traces lineage as a descendent of the first widespread browser Netscape.
- Chrome - Google supported browser, very fast, portal to bring users into other (non-FOSS) Google services.
 Web Conferencing
- BigBlueButton - standard FOSS conferencing app for education.
- DimDim - one of the first FOSS conferencing apps.
- WebHuddle - one of the first FOSS conferencing apps.
 Website Content Management Systems (CMS)
- Drupal - most widely used FOSS content management system for complex sites, many themes and plugins.
- Joomla - second most widely used FOSS content management system.
 Website Development
- Amaya - original browser supported by creator of web, Tim Berners-Lee, with his vision of always being able to both view and edit any page in the same app.
- Bluefish - editor.
- BlueGriffon - editor.
- DRKSpiderJava - Multiplatform Website crawler and link checker.
- WordPress - standard and most widely used FOSS website software, large set of templates, support for blogging, discussions, forums.
- MediaWiki - original and same software that runs Wikipedia.