Rails 3 has been out quite a while in "rails" time. Back in the world of rails 2 most custom code was added via rails plugins stored in the vendor directory. Although this allowed for a clean dependency relationship when new versions of plugins came out it made it difficult to upgrade existing code bases. So when it came time to upgrade to rails 3 this contributed to a lot of people having difficultly upgrading their existing codebases. Along came the new revised rails 3 engine...