Since 1977 when I first got my hands on Traveller (geez... that was a long time ago...) I have started off at least a couple of times writing my own mapper/system generation application starting with the TRS80, later the Sinclair and even later still the Commodore 64. Every time I start the process on Linux I seem to lose interest, get too busy with other things or otherwise get distracted from the task.
My latest thinking has been to write one in Java so it can run on many platforms (notice I said "many") and every time I start with that idea I say to myself "oh God... not that again" :-)
Just getting readable, nice looking hex maps seems to get in my way every time.