AberSim is a simulating and development environment for the Motorola 68HC11 processor. I've been putting it together for myself and the other GNU/Linux users at UWA. I'm using as11 from Motorola as the assembler and sim68xx as the simulator, both are included in the download packages. It's only had a few days work on it, so is somewhat buggy and incomplete, but there's enough done to have a play around with. More details about my plans for AberSim and what I'm currently working on can be viewed on my development log.
Currently it has problems with programs starting at a location other than 0000, so for anyone doing worksheet 1 from CS234 change "ORG $E000" to "ORG $0000" and it'll run fine. Also closing the listings window will cause it to crash.
Warning: The next version is likely to break compatibility with previous versions. I'm switching over to using the GNU m68hc11 binutils for better error output and more Freedom.