| Gem | Description | Notes |
|---|---|---|
| rbconfig | Reflection on configuration | Builtin > 1.8.7, see http://rbjl.net/35-how-to-properly-check-for-your-ruby-interpreter-version-and-os |
| railroady | GraphViz bases Classgrapher | Recommended in CS169.2x |
| RedCloth | Textile | Used in typo, CS169.2x |
| omniauth | SSO OAuth etc | Google, Twitter, Facebook… CS169.2x |