3. RemarkerclustererREMarkerClusterer creates and manages per-zoom-level clusters for large amounts of markers.
6. ReswitchOpen source alternative to UISwitch, customizable via UIAppearance protocol.
11. Reactivityviewcontroller[DEPRECATED] Open source alternative to UIActivityViewController, highly customizable and compatible with iOS 5.0.
13. RetrimcontroliOS audio trim control, similar to the one seen in default iPhone Voice Memos app.