The application process of Google Summer of Code requires students to make a small contribution to the project(s) of their choice to demonstrate that they are capable of making a change following the upstream submission procedures. In my understanding, this is less about the actual code than it is about demonstrating these skills. This is (partly, the other reason being that as I was working on these proposals I was also finishing up several course projects) the reason that the contributions here are rather small:
For GNOME Calendar I fixed the drag and drop mouse cursor when moving events around to show an arrow indicating a move as opposed to a plus.
For Mutter I implemented a fallback to a texture cursor in case the hardware cursor isn’t available.
For ratbagd’s Python bindings I implemented exception catching for some DBus exceptions, which would otherwise crash Piper when ratbagd wasn’t running.
I got accepted for 2017’s GSoC and kept a blog on my progress. You can read the introduction here; an overview of the complete series can be found here.