I've been fiddling with
KloogeWerks on and off for a year or so, although I've never actually used it in anger. It's a very cool tool, tons of features, nice look n feel, marred only by the fact that it doesn't have a complete "definition file" to enable you to play BRP out of the box. I've been hacking one up myself which is semi-usable, but it'd be cool to see a fully-featured one hit the shelves. Maybe one of these days, when I have some time...
Cheers,
Sarah