VSTa

VSTa (short for Valencia's Simple Tasker) was a self-hosting microkernel operating system build in the 1990s. It had a lot of novel ideas, a simple and elegant kernel, and featured user-space device drivers and filesystems. Unusually, it also had a kernel debugger so if anythign went wrong it would drop into the debugger instead of just giving a kernel panic message.

It had a services model inspired by Plan 9, and had a largely complete GNU toolchain so it was capable of building itself. I was largely active in updating libc, porting tools, writing drivers, and performance tuning the kernel form 1993 to 1995.