A UNIX-like x86 operating system created from scratch. It has a virtual filesystem with ext2 support, memory allocation and management, basic multitasking, and a basic shell interface that runs in the kernel.
A work-in-progress "game" where you can program virtual robots in assembly. It's made in C++, and right now there's an assembler and virtual CPU emulator, which can interface with virtual hardware and memory. It's pretty neat, you should check it out.
Probably one of my biggest codebases - it's a Minecraft-like voxel game that was made completely from scratch in Java and OpenGL. It supports multiplayer over the network, dedicated servers, and at some point I was working on infinite worlds but abandoned that after I moved on to other projects.