What license should I choose?

It is very important to take some time and think about what you are trying to achieve with your project.

As the Linux.com article on Choosing an open source license points out, the impact on derivative works has to be considered when choosing the license. For example, choosing the GNU General Public License, all derivative work must be GPL as well. A good overview of the options is provided in Appendix A of the paper The Need for Open Source Software in Machine Learning by Sören Sonnenburg et al.

For the impatient, you can use the ChooseALicense.com website (run by GitHub) to quickly determine an appropriate license for your project.

A complete list of approved open source licenses is available on the Open Source Initiative website. Wikipedia lists open source licenses as well.