Most mission editors are based in DOS or Windows and are limited by the peculiarities of these environments. I decided I wanted one that was limited by the peculiarities of Linux and X windows.
I started near Halloween of 1994 with Linux 1.1.59, G++ 2.6.2, XFree86 3.1, and FWF 3.47(?).
2 months and 20000 lines of C++ later, the Purple Frog Mission editor alpha release 1 was made available to a select group of suckers. Like all software, it sucked. However, it is improving.
As of June, 1995 it is in Beta release 1. I consider it somewhat usable, although your questions and requests may drive me to improve it. I want to add context-sensitive help, but Purple Frog is taking me in other directions so hacks won't be happening as fast as they used to.
It is most similar to the mission editor DEU by Raphael Quinet (there are accents in there somewhere) and friends. Unlike its cousins based in non-operating-systems, it handles editing of multiple missions at the same time, and handles multiple views of the same mission at once.
The distribution site for the PFME is here.
Have a screen dump.
Purple Frog Software