LibHealComm-4.0 is a library that keeps track of heals being cast by both the player and the people they are grouped with. It will estimate how much a heal will land for using talents, glyphs, auras as well as gear and provides data to other users using LibHealComm-4.0. There is a variety of ways to show data, anything from a simple bar that indicates how much healing is incoming on an unit to showing a graphical summary of what player is casting what heal, on who and how long it will take to land.

Thanks to xbeeps for his work on LibHealComm-3.0 as well as Gagorian (DrDamage) for being able to steal his data.

For tickets, http://www.wowace.com/addons/libhealcomm-4-0/tickets/
For discussion, http://forums.wowace.com/showthread.php?p=286168

Documentation

Documentation for LibHealComm-4.0 can be found here

Accuracy

Blizzard still does not specifically send the GUID that a cast is on, while LibHealComm-4.0 is 100% accurate if the user is healing through click casting or normal means and it's 99.99% when using others there is still a very (very) small chance that it will not find the GUID. If it does manage to not find the GUID it will make the best guess it can off of the name.

Addons supported

Injector, Shadowed Unit Frames, Pitbull4, Vuhdo, VisualHeal, PerfectRaid, X-Perl, Grid2, BobsToolbox, Stuf Unit Frames, oUF (with oUF_HealComm4 plugin + support), HealAssign, Grid, IceHUD

Spells supported

Druids: Nourish, Healing Touch, Regrowth (And the HoT), Rejuvenation, Tranquility, Lifebloom (And the final heal), Wild Growth
Paladins: Holy Light, Flash of Light and heals casted by Beacon of Light
Shamans: Lesser Healing Wave, Healing Wave (Including glyph), Chain Heal (first bounce only), Riptide, Earthliving Weapon
Priests: Penance, Renew, Flash Heal, Greater Heal, Prayer of Healing, Lesser Heal, Heal

What's different from 3.0?

3.0 is based on using names to identify who casted a heal as well as the heals targets, while names give you decently accurate information it is not 100% and most addons use GUIDs rather then names to identify people. 4.0 also has a more up to date spell database and supports the more unique healing mechanics that were added in Wrath of the Lich King such as Glyph of Healing Wave, Beacon of Light and hots in general.

But what about users who are using 3.0?

To make moving to 4.0 easier for users (and so they don't complain to authors about missing data!) there is a small wrapper library you can embed along with 4.0 that will catch data sent for LibHealComm-3.0 and update the players local healing data in 4.0, it will also handle sending healing data but this can be disabled with a function call.

More information on the wrapper library can be found at http://www.wowace.com/addons/libwrapperhealcomm-1-0/ while this library is optional, it is suggested that you embed it so that users are not using exclusively 4.0 data.