Easily write arbitrary filters

Debugging toolbar for Rack applications implemented as middleware. Based on logical-insight and rack-bug.

Record Cache for Rails 3

This gem makes Rails console sessions less dangerous in specified environments by warning, color-coding, auto-sandboxing, and allowing read-only external connections (disables job queueing, non-GET requests, etc.)

A nifty service layer for your Rails app

Enable using native sql enums

It makes working with pure SQL easier with syntax highlighting. Let's you clean your Ruby code from SQL strings.

Enhanced AJAX handling for Rails apps.

An Active Admin plugin to add dynamic behaviors to fields

UI interface for rails-settings-cached in active admin

Simulate multi-table inheritance for activerecord models using a polymorphic association

MySQL index hint support for ActiveRecord

Represent ActiveRecord Markdown, Textile, RDoc columns as Markdown, Textile, RDoc objects using various external libraries to convert to HTML.

Fast Rails serializer with built-in caching

Cape dynamically generates Capistrano recipes for Rake tasks. It provides a DSL for reflecting on Rake tasks and mirroring them as documented Capistrano recipes. You can pass Rake task arguments via environment variables.

A gem to manage Cassandra database schema for Rails. This gem offers migrations and environment specific databases out-of-the-box for Rails users.

Faster implementation of Haml template language.

https://github.com/tsukasaoishi/fresh_connection

Another business actions architecture for Rails apps

lazy_migrate lets you easily see which migrations have and have not been run, and makes it easy to up/down/migrate/rollback your migrations through a terminal UI. You can even bump migration versions in the event that you've just pulled master and somebody else merged their migration before yours.