UITableView subclass that abstracts away the ugliness involved with creating static or modular UITableViews. Settings and menu pages are a snap to create with DAModularTableView.

An example application that shows how to get Paperclip and SWFUpload playing together nicely.

A concise routing library for Ring/Clojure

Multi-model forms plugin for rails

Easy file attachment management for ActiveRecord

a better version of this functionality is in rails 2.3. use that!

Ruby-like hybrid OOP/functional programming language for BEAM, the Erlang VM

Open Source Social Network written in Ruby on Rail by Less Everything

Resource-oriented open source Ruby framework for Web apps.

ActiveRecord connection proxy for master/slave connections

AASM - State machines for Ruby classes (plain Ruby, ActiveRecord, Mongoid, NoBrainer, Dynamoid)

Merb Core: All you need. None you don't.