So I've looked through my project archives and I was unable to find the original source code I made for the video tutorials of the OpenTK Platformer Tutorial Series. However I did find a working copy of my example I made off stream beforehand to work out the bugs. It should be quite similar to the original video series' code and if you're looking for something to to mess around with it should do the trick:
2016 Gallery 3: The Last of OpenTK
After struggling with the speed of OpenTK I worked on only a couple other projects before finally moving on. These were the last things I ever made in OpenTK
I wanted to try my hand at method for "Triangle Soup" vs. sphere collision detection. I got to the point where I had divided the levels triangles into a quad tree and tested moving the sphere around and seeing which triangles it would have to do intersection tests with
I also worked on a 2D snake game for a demonstration. It was a simple snake game with a couple more features not shown here. It had a grid that moved like Geometry wars and bombs that would spawn that you would have to dodge. It was a fun game to show people and mess with the settings (speed, spawn-rate, etc.)