This page collects good FOSS system software – operating system, middleware, utilities – everything not applications. Please make sure software you add has current development and user communities – any size, just current! If software that meets this threshold later falls out of use, please keep it on the list for historical and reuse purposes, with the label (Not Current).
- Puppet – automated installation, configuration, management, etc.
- Amanda – most widely used FOSS backup software.
- Bacula – second most widely used FOSS backup software.
 Bug Tracking & Management
- BugZilla – standard FOSS bug management app, traces its heritage back to Mozilla Netscape.
- Entomologist – coordination of multiple bug trackers.
- Memcached – memory caching.
 Certificates – Digital, SSL
- Dogtag – enterprise-class Certificate Authority (CA), hardened by real-world deployments, supporting OCSP, smartcards, and more.
- easy-rsa – OpenVPN utility to build and manage a PKI CA, create a root certificate authority, and request and sign certificates, including sub-CAs,
- EJBCA – Certificate Authority and OCSP support, using Java, high performance, highly scalable, platform independent.
- OpenCA – robust, out-of-the-box Certification Authority with full-strength cryptography, based on openLDAP, OpenSSL, Apache Project, and Apache mod_ssl.
- OpenSSL – robust, commercial-grade, toolkit implementing Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1), and a full cryptography library.
- r509 – Ruby gem using OpenSSL for creation of signed certificates, CSRs, and revocation (CRL/OCSP), for full RFC 3280/5280 certificate authority enterprise use.
- TinyCA2 – fork of the no longer maintained TinyCA, manages a certification authority and x509 certificates as a frontend to OpenSSL, including subCAs for more complex setups.
- XCA – for creating and managing X.509 certificates, certificate requests, RSA, DSA and EC private keys, Smartcards, CRLs, and sub-CAs.
 Cloud Computing
- eyeOS – Cloud operating system.
- OpenStack – original FOSS cloud IaaS project.
 Cloud Management
- Deltacloud – an abstract cloud management layer.
- Juju – management of cloud services (from Canonical/Ubuntu).
- jclouds – abstracts multiple cloud API's with Java.
- Libcloud – a library that abstracts multiple cloud API's.
 Collaboration Server
- 7-Zip – standard gzip, zip, other compression.
 Configuration Management
- Git – highly scalable, developed by Linux creator Linus Torvalds.
- Subversion – one of the first FOSS CM apps.
 Cross Language Development
- Finagle – Twitter network stack for the JVM to build asynchronous RPC clients and servers in any JVM hosted language.
- Drizzle – MySQL fork.
- HyperTable – very high scalability Hadoop compatible distributed database.
- MariaDB – MySQL replacement.
- Membrane SOA Registry – a registry for SOA services.
- MongoDB – scalable NoSQL database.
- MySQL – popular relational database.
- PostgreSQL – standard FOSS enterprise relational database, very highly scalable.
- Neo4j – high-performance, NOSQL graph database.
- Perst – object oriented embedded database.
- RavenDB – document database.
- Redis – in-memory key value data store.
- Riak – fault tolerant distributed database.
- SQLite – light-weight relational database.
- Voldemort – distributed database.
 Database Management
- phpMyAdmin – one of the first GUI tools for DB management.
 Data-Center Management
- DWR – Ajax Java library.
- Bootstrap – Twitter framework for web development.
- Jaxar – Ajax server.
- Ruby on Rails – supports very rapid web development.
- FreePascal – A FOSS Pascal editor/compiler like Turbo Pascal that runs on multiple operating systems (Linux/FreeBSD/Mac OS X/iOS/Darwin/DOS/Windows ...) and architectures (Intel x86, AMD64/x86-64, PowerPC, PowerPC64, SPARC, and ARM).
- Lazarus – Lazarus is a GUI editor like Delphi and uses the FreePascal Compiler. Write once compile anywhere.
 Directory Services
- OpenLDAP – standard FOSS Light-weight Directory Access Protocol (LDAP) solution.
 Disk Partitioning
 Distributed Computing (High Scalability)
- Cassandra – distributed data replication and fault tolerance.
- Hadoop – processing of very large data sets across many computers.
- Mesos – application resource management across clusters.
- Spark – high scalability distributed data analytics.
- Storm – distributed very large data set processing.
 Domain Name System (DNS)
- BIND – manages the relationships between domain names and IP addresses, pretty much runs the Internet.
- Linux drivers – drivers for printers, scanners, and other hardware devices for Linux operating systems.
- Davmail – Microsoft Exchange connector for almost any client.
- Dovecot – standard FOSS email server with IMAP, POP3 support.
- DSPAM – content-based adaptive spam filter for multi-user enterprise systems.
- OpenDKIM – DKIM (Domain Keys Identified Mail) sender authentication system (RFC6376), includes Author Domain Signing Practises (ADSP, RFC5617), Vouch By Reference (VBR, RFC5518), and Authorized Third Party Signatures protocol (ATPS, RFC6541).
- Postfix – standard FOSS Mail Transfer Agent (MTA).
 File Encryption
- End-to-End – email encryption plugin for Chrome web browser.
- FreeOTFE – old FOSS on-the-fly disk file encryption.
 Enterprise Service Bus
- HylaFax – fax send, receive, route to email.
 File Synchronization
 File Systems
- Ceph – distributed object store and file system.
 File Transfer Protocol (FTP)
 Geographic Information Systems
 Groupware Synchronization
- SyncEvolution – synchronizing with Evolution email / calendar / contacts app.
 Messaging Systems
- RabitMQ – application messaging.
- Red5 server – flash video emulator.
- Tizen – device API for HTML5.
 Natural Language Processing (NLP)
- Linux Wireless – IEEE-802.11 subsystem.
- OpenDayLight – software defined networking (SDN).
- Samba – connection of Linux and Microsoft Windows networking, file systems, printers.
 Network Management
- Nagios – standard FOSS monitoring and alerting software.
 Network Monitoring
- WireShark – IP network packet inspection.
 Operating Systems
- Contiki – lightweight OS for the "Internet of things".
- Linux – FOSS version of Unix, now the standard and most widely used server operating system.
- Red Hat – first commercially supported Linux operating system (1993).
- Tails – Secure Linux bootable from USB with privacy tools builtin.
- Ubuntu – most widely used FOSS desktop operating system.
 Operating Systems Embedded
 Operating System Emulation
- Wine – Windows emulator on Linux, can run some but not all versions of a lot of Windows software.
 Operating System Virtualization
- OpenVZ – Linux kernel parallelization.
 Password Utilities
- Offline Windows Password & Registry Editor, Bootdisk / CD – Win NT 3.5 through Windows 8.1 (GPL)
- ophcrack – Windows password cracker using rainbow tables (Apache 2, GPL2)
- Liferay – mobile content development.
 Proxy Servers
- Nginx – HTTP and reverse proxy server, and mail proxy server.
 Security Software
- Barada – two factor password authentication.
- Kerberos – standard FOSS software for secure authentication of users and software.
- monkeysphere – management of networks of trust.
- OpenVPN – standard FOSS software for virtual private networks.
- CyaSSL – certificates.
- Android – standard FOSS smartphone software from Google.
- Funambol – standard FOSS smartphone system and software communications integration software.
 Spam and Anti-Virus Protection
- ClamAV – standard FOSS anti-virus tool, mainly used to clean Windows viruses from email passing through.
- ClamWin – ClamAV version for Windows computers.
- dkim-milter – legitimate email authentication support.
- domainkeys-milter – legitimate email authentication support.
- DSPAM – standard FOSS spam blocking software.
- StatsD – front-end proxy for the Graphite/Carbon metrics and graphing server.
 Storage Management
- FreeNAS – Network Attached Storage (NAS) management.
- OpenFiler – NAS and SAN storage appliance.
 System Cloning
 System Integration
- Chef – automation of application management and configuration.
 Systems Management
- Spacewalk – Linux content provisioning and monitoring.
- sysdig – capture and analyze Linux instance state information.
- ZooKeeper – centralized maintenance of system configuration data, Apache project.
- Chaos Monkey – random process termination testing (from Netflix).
- Funkload – web application testing.
- HtmlUnit – GUI-less web emulator for testing from Java.
- Iago – load generator for performance testing.
- Selenium – automated web testing.
- StressLinux – hardware stress testing.
- Zipkin – web service response time profiling.
- WebM – an open web media project developing a high-quality, open video format.
 Virtual Desktop Servers
Also see Virtual Desktop Clients.
- FreeNX – the first NX server built on NoMachine's original FOSS release.
- neatx – an NX server from Google.
- SPICE – NX software originally developed by Redhat.
- x2go – X-windows remote access.
 Web Server
- Apache Web Server – the first and now standard FOSS website server, runs most of the world's websites, provided an early proof of the superior performance and robustness of a FOSS application.