The first subpart of my GSOC 2018 project was working on feature to rotate models based by selecting a face. After working on it for while, it, was merged into master. Unfortunately, a few bugs crept through, but were quickly caught by the community and then fixed.
After that I attempted and failed to solve some minor bugs (one of which I encountered earlier in the summer).
Then I moved on to the next large subpart of the summer, working on porting the 3d views from Perl to C++. While I made good progress on the 3D plater, there are still a few things that are a few inconsistencies between the Perl and C++ 3D platers. I moved on to the other 3D views, the cut dialog and 3D preview, but made only a little progress on them because other things needed to be ported first. Ultimately my work in progress was merged into the porting branch (cppgui).
Next was porting smaller sections of code. These were mostly pretty straightforward conversions.
The final subpart of the summer was working on getting a system for converting lines into arcs for better GCode output. This has been a long standing issue; recently, it was somewhat revived with the work of PurpleSensation. My goal was to (partially) implement the algorithm he proposed in his paper and integrate it into Slic3r. I didn't achieve as much of this implementation as I had hoped; it is currently very buggy. However, it can be a good base to be built off of.