Some things I'm currently working on:
A Linux-based partitioning hypervisor for real-time and safety scenarios
A real-time networking stack for Linux RT extensions
Xenomai (various contributions, RTDM maintenance)
Real-time framework for Linux
Processor and hardware emulation
The Linux hypervisor, specifically nice for running virtual PCs on your desktop, cloud server, PBX, industrial control system, ...
And a few noteworthy projects of the past:
IrCOMM support for Windows sucked (some say it still does), this project aimed at improving the situation.
Serial Port Laser Link (German)
Those were the times when WLAN didn't work yet, flat rates weren't affordable and your friends lived next house.
Elevator Simulation (German)
First Java stuff back in study times, nice to see it's still running.
(there is some more weird stuff on my attic, just have to remove the dust)