RaidCooldowns came about after a guild leader complained that oRA2 didn't track all of the raid cooldowns he wanted to know about, and those it did track were unreliable because not everyone ran oRA2. It consists of two separate addons.
NOTE: This addon requires RaidCooldowns, located here
RaidCooldowns_Display is a highly customizable bar display of your raid's cooldowns. It tracks Rebirth, Reincarnate, Shield Wall, Blood Lust, Innervate, Divine Intervention, Soulstone, and many others. Adding a new cooldown to track is generally no more than one line of code. Most of the time, RCD_Display will track cooldowns via combat log events. However, some spells can't be tracked this way due to limitations in the WoW API. For those spells - Rebirth, Reincarnate, Divine Intervention and Soulstone - RaidCooldowns_Display can receive syncs from members running either oRA2 or RaidCooldowns.
RaidCooldowns is a lightweight method of syncing those cooldowns that can't be detected via the combat log. It's a good alternative if you have a stingy Druid who doesn't want to run the entire oRA2 package just so you can know his Rebirth cooldown. Better still, RaidCooldowns will broadcast to both RCD_Display and oRA2, so people running oRA2 but not RCD_Display aren't left out of the loop.