Both from my own experience and from a number of other reviews I've read,
Daedelus sems to be the least bad of any software available, and it's
available in both mac and IBM formats. It has invention heuristics,
revision guide questions, and network collaorative editing systems (not
much use if you've only got 2 computers, but there it is.)
I have their address at work--I'll send it.
Beware of idiot grammar-handbook-in-a-box programs. But I don't need to
tell you that.
Style checkers are also popular but they only work for people who already
kno what they're doing. Much of their advice is unhelpful and some is
absolutely wrong. But since students oftem meet them, some part of me
says that they should be exposed to them when there's someone around to
start a discussion of what's right and what's wrong with the specific
pieces of advice they throw up. (No pun intended but maybe there should
have been.) They could be great group conversation starters. Grammatick
IV is the least bad I've seen. It's built into Word Perfect 6.