The <ahref="licenses/mit">MIT License</a> is a permissive license that is short and to the point. It doesn't include any warranties and lets people do anything they want with your code (with attribution back to you).
The <ahref="licenses/apache/">Apache License</a> is a permissive license similar to the MIT License, but also contains a patent license for any code that infringes on a contributor’s patents.
The GPL (<ahref="licenses/gpl-v2">V2</a> or <ahref="licenses/gpl-v3">V3</a>) isn't a permissive license, meaning that it requires that folks who modify your code also license their changes under the GPL. V3 is similar to V2, but adds a restriction restricting use in hardware that forbids software alterations.