Free software, software libre, or libre software is computer software that gives users the freedom to run the software for any purpose as well as to study, modify, and distribute the original software and the adapted versions. The rights to study and modify free software imply unfettered access to its source code. For computer programs which are covered by copyright law this is achieved with a software license where the author grants users the aforementioned freedoms. Software which is not covered by copyright law, such as software in the public domain can also be free if the source code is in the public domain (or otherwise available without restrictions). Other legal and technical aspects such as software patents and DRM may impede users from exercising these rights, and thus prevent software from being free. Free software may be developed collaboratively by volunteer computer programmers or by corporations; as part of a commercial activity or not.