Google Summer of Code

Google Summer of Code (or GSOC for short) is an annual open source program where Google connects mentors at large and popular open source projects to contributors and provides a stipend to those who finish their contribution. The website for more information is here. If you don't have anything to do over the summer, it can be a great way of getting your hands dirty with software development while also being able to get experience with a large open-source contribution.

Timeline

You can find the timeline here. However, it is very important to get connected with the organization and/or mentors earlier than the deadline to talk with them about the feasibility of the project and to show your interest.