GPL. I'll try it. I wish someone would recreate something like WordPerfect 5.1 as an OS X Cocoa app around the LaTeX layout engine. It wouldn't be a "port", more using WP 5.1 as a functional spec. It would not support all of WP 5.1's features of course. It might, however, be the savior for those of us who loathe Microsoft Word. (Since WordPerfect used internal markup, the functionality may be more compatible than one might expect. Remember "reveal codes"?)
PS. Thanks Alexandre A. for pointing me to the great wikipedia article on LaTeX.