I've been thinking lately about replacing my time-wasting games with free software variants, partly because I support free software and it gives me warm, fuzzy feelings, and partly because I know that one day my old copies of JezzBall and Chip's Challenge and such just won't work very well on my new computers.
I stumbled, by chance, across Wikipedia's entry for JezzBall, which mentioned some clones. I looked into them, and decided to download and try out the first one that I found which had a Windows port: IceBreaker. It's been a few years since it's been updated, but it is still a pretty cool clone. There are several differences between IceBreaker and JezzBall in gameplay, scoring, and appearance, but the changes aren't so great that it isn't still a fun game. One thing that I did enjoy is that the beta version of IceBreaker is skinnable, and comes with several skins; you can set it to random and just enjoy the variety.
I'll have to see if I can find clones of the other games from Microsoft's Entertainment Packs--several of them were very enjoyable ways to waste a few minutes, and deserve to follow me through computer upgrades. I seem to recall downloading at some point a very good Chip's Challenge clone, so I'll have to see if I can dig that one up as well.