You’ve probably seen some variation of these popular licenses:

• BSD (Original, Modified, Free)
• ISC
• MIT (Expat, X11)

What’s the difference between them?

BSD

The Original BSD license, can be used as a permissive license that is similar to the MIT license but with additional requirements regarding advertising and name reuse. The original BSD license is also known as the “4-clause BSD license”. You should use the Modified (3-clause) BSD license in place of this license for GPL compatibility.

Unlike the Modified BSD license, the Free (2-clause) BSD license ,omits the non-endorsement clause, as well as adding a disclaimer about views and opinions expressed in the software. This license is also known as the Simplified BSD License.

ISC

The ISC license is another permissive license. This license is also known as the OpenBSD license. Like Modified and Free BSD, it is compatible with GPL. This license is equivalent to the MIT or Free BSD licenses in function, but omits some language deemed unnecessary. Although brief, there are some issues with wording in this license. To avoid issues with the wording in the future, it’s recommended to use another license.

MIT

There are two licenses that are typically referred to as “the MIT license”. These are the Expat license and the X11 license. The Expat license is a permissive, GPL compatible license. This license is similar to the ISC license but worded to resolve ambiguities. Unlike the Expat license, the X11 license forbids exploiting the names of copyright holders.