Commercial Open Source Software
FOSS can be sold and often is, for example with support agreements including telephone and rapid patch response, or with services agreements to match configuration to an organization's process workflow. And there isn't anything wrong with that according to most FOSS licenses. Indeed, to this day the primary product of RedHat the most commercially successful open source company ever, is the FOSS operating system Linux.
Commercial Open Source Software (COSS) often contains elements of FOSS, however it also limits availability of some enhanced functionality to closed proprietary software, thereby creating a potential path to the same old vendor lock-in, and so does not qualify as FOSS as a whole.
"Dual-licensed open source" is an administration method whereby companies provide software with open source licenses and also license the very same code with a proprietary license for organizations whose procurement systems require one. The principle with dual-licensed software is the same: it can be FOSS if all versions are made available in a FOSS license approved by the OSI.
Some examples of COSS are listed below. (Please only add links below to pages describing closed software requiring fees).
- ConcourseSuite (formerly Centric)
From COSS to FOSS
Companies that thought about COSS but then decided FOSS was the better strategic decision: