The first DOOM Episode (of several levels) was shareware and therefore highly encouraged to be shared however seen fit, whether for free, copying from BBS's, FTP, USENET, or on pay-for compilations or stand-alone copies. The full game was $29.95.

Mega Man Legends 3 Prototype Version will not be shareware, of course, but it is supposed to have over five hours of gameplay and let you roam about the unfinished areas with a debug mode. For $2 that's a lot better than a game rental in my opinion.