What Is Open Source?
The open source movement began as an offshoot of the free software movement, aimed at making free software more appealing to commercial interests. The problem is that the English language overloads the term free with two very different meanings, referring to freedom and to cost. Members of the free software movement commonly distinguish between these two meanings by referring to free software as "free as in speech," and not "free as in beer."
The general perception of free and open source software (FOSS) comes from a few high-profile projects, such as Linux. They are perceived as being written by hobbyists working for free, and to cost nothing. But neither of these perceptions is either required or implied by either the free software or open source definition.
For software to be classed as free software, the user must be able to do all of the following:
- Run the software. This right is obviously a necessity for any software to be useful.
- Modify the software. Less obvious, but equally essential. Much commercial software grants this right to a limited extent; for example, Microsoft Office can be extended by using VBA. The difference with FOSS is that the customer, not the supplier, determines the permitted extent of the modifications.
- Redistribute the software and modifications to the software. Important from a cost perspective. If you can't distribute your modifications, other people can't benefit from them. More importantly, you can't benefit from their modifications. If two customers need the same feature, they have two choices: both can add the feature (duplicating effort), or both can wait for the supplier to add the feature, and then both can pay to upgrade.
Open source software grants similar although less concisely defined rights. (The difference is the motivation for the software, rather than the rights themselves. In general, the terms open source software and free software can be used interchangeably.)
Note that these rights apply only to the customer, not to the world at large. If a company commissions custom software and has all of these rights assigned to that software, it's qualified as FOSS, even though the software may not be distributed.