I was talking to Tim the other day about auditing Rails projects, and how we see a lot of Rails projects that reinvent the wheel instead of using plugins. The obvious follow-up question, of course, is "What plugins (or gems) should we be using?" Below I list ten plugins that we use regularly, and a brief reason why you might want to, too.
Many of these plugins have alternatives (e.g., you could use rspec instead of test_spec, or nulldb instead of unit_record). Regardless of which plugin you pick, make sure you think about the features provided by the plugins above, and don't reinvent the wheel.
Notice that most of these plugins are already in git, so forking them is easy. If you see something that needs improvement, jump in and do it! While reinventing the wheel is bad, improving the wheel is most welcome.
[6/18/2008: updated to include github url for fixture_replacement]