Wikia is very public. It also runs on MediaWiki, which is very non-lightweight, though I suppose that is beside the point if you do not have your own webspace.
I am not a fan of Bugzilla, mostly because it is pretty unintuitive. It is, however, a pretty effective system if everyone on it figures out how the heck to use it (ha!), looks for their problem before they repeat a report (ha!), there are lots (i.e. hundreds or thousands) of potential problems, and you have multiple developers who can fix things (ha!).
For one-man projects, I think small wikis can be much better, mostly because they allow you to merge, delete, and search without having to learn what goes where in the interface before you can even touch a durn thing; plus you can fix up what someone else says if you need to (which comes in handy for both developers and bug reporters).
All you need is a wiki package (like DokuWiki), and somewhere to host it (don’ lookit me! nothing personal, just can’t afford to host a romhack anything at the moment).