Theme Hospital
For the past two months or so, one of my side projects has been writing an open source clone of Theme Hospital. I recall Theme Hospital as being one of the great classic games I had when I was younger, and it's sad to watch it slowly become harder and harder to play on modern operating systems, with modern hardware, and with modern conveniences (like 3-button mice, screen resolutions larger than 640x480, and so on). A game like Theme Hospital really deserves a decent open source clone, and so I thought I'd have a stab at making one.
You can find downloads, source code, an issue tracker, etc. over at Google Code if you're interested.