Open-source licences (MIT, Apache, GPL)

In short: Open-source licences allow source code to be used, modified and passed on under certain conditions. They differ mainly in whether changes must remain open.

In more detail: Permissive licences (MIT, BSD, Apache 2.0) allow almost everything, including in closed software, as long as the licence notice is kept. Copyleft licences (GPL, AGPL) require derived works to be disclosed under the same licence.

Not legal advice.

In Depth

• MIT: very short, almost no obligations.
• Apache 2.0: like MIT, plus an explicit patent licence.
• GPL: Whoever builds GPL code into a program and distributes it must offer the source code under GPL.
• LGPL: weaker copyleft; linking as a library is possible under conditions.
• AGPL: Even with use over the network (web service) the code must be open.
• No licence: By default copyright applies: use is not permitted.
• Checking: Check dependencies for licences before you sell a product.
• Attribution: Licence notices belong on a “licences and sources” page (licences).

See also: Licences, Copyright, Open Source