Creative Commons is a nonprofit organization that has created a set of free and easy-to-use prefabricated licenses that you can apply to your work. These licenses allow you as an author to retain all of your rights while allowing specific types of reuse by others without them having to seek your permission first. 

Graphical representations of the six Creative Commons licenses.

Open Source is a similar concept to Open Access (OA), except that it applies to software programming and code rather than to other more traditional works. There are a variety of open licenses available to share source code, and the Open Source Initiative (OSI) has compiled a list of reputable options.