Video game development is a just a hobby for me as well (I did have a taste of doing it professionally at one of my jobs, but they went under unfortunately). Many of my projects go unfinished, but I have completed a few. Some of the cooler ones include:
1) Re-wrote several of the classic Atari games in BASIC (not an Atari emulator, but the individual games themselves)
2) Re-wrote the original Super Mario Brothers in Visual C++ for my college honors project (was so dead-on even to the sound effects, that people were asking if the project was an NES emulator. I had a 3-inch thick printout of the source code to prove that it wasn't
)
3) Wrote a card-game engine which is the base code for numerous professional computer card games, including "Magic the Gathering" and "The Highlander"
4) Wrote a 3D sound engine that is currently being used in several games, including "Minecraft"
