Ruby on Rails acts_as (the good ones I've heard about)
| acts_as_authenticated | An authentication system |
| attachment_fu (supersedes acts_as_attachement) | File uploading made easy |
| acts_as_versioned | Automagic versioning system |
| betternestedset (supersedes acts_as_nested_set) | Super tree structures (threads, hierarchy, ...) |
| acts_as_taggable_on_steroids (supersedes acts_as_taggable) | Tag your datas ! |
| acts_as_plugin | Learn to write your own plugins |
| acts_as_tsearch | PostgreSQL tsearch interface |
| acts_as_suggest | See google "Did you mean?" |
| acts_as_ferret | Interface with the Ferret search engine (a Lucene ruby port) |
| acts_as_list | Ordered lists (from Rails Core) |
| acts_as_polymorphs | Two sided polymorphic associations |