Mappy is closed source so you cannot quickly adapt it to your engine, it will always be a generic map editor and you have to write external converters/tools if you want more.
Actually...
The code was made freely available for anyone to use and/or modify a long, time ago. So, you can adapt it and make it as "non-generic" as you want. All the original author asks is that you give him credit and NOT name your resulting editor "Mappy".
FWIW, I just downloaded the source for Mappy 1.01 and found that it still compiles just fine on Ubuntu 10.10. (As long as you don't mind ignoring the 384 warnings issued by the Allegro libraries for using deprecated code <grin>). It runs natively on Linux, loads fmp files, etc.
There is actually a more up-to-date version of the source available, but it's for the Windows version. I haven't tried to compile it yet.
Todd