hi glonch, welcome to the site.
i think given the nature of this site, there is almost no idea for a program that won't be interesting to at least some people.
and there's nothing wrong with working on programs just for the fun of it.
keep in mind there are some powerful programs to do this already (and some papers on good algorithms for it), though i don't know any off hand. maybe others can post some links.
so is your question about cross-platform programming tools? (you mentioned you wanted it to run on windows/linux/mac.
there are cross platform Basic interepreters (Mark0 might have some hints there). Then there are all the scripting languages which might be a good match for this. depends if you want graphics or not.