DamageMeters 

Maintainers:
Up to 5.8.3 was AnduinLothar
Up to version 5.0.0 was Dandelion

Summary:
DamageMeters monitors damage and healing done by and to yourself and other nearby players. It keeps a running total for each player and displays the information as a bars chart in a frame on the screen. It is perfect for real-time comparison of the various members of your party or raid. At any time the text results can be output as "says", to raid or party chat, or whispered to another player. Many console commands exist for customizing the meters: type "/dm help" for a listing.

FAQ:

Q: Why the "-AL"?
A: Dandelion, the orig author, has retired from WoW. AnduinLothar (me) modified v5.0.0 from Cosmos because that version works with English, German and French clients. AnduinLothar has no long term plans to enhance functionality and would gladly hand over maintenance to someone else, but decided DamageMeters had a large enough user base that it deserved to be updated to use the 1.12 addon communication API.

Q: MY DM WINDOW DISSAPPEARED!
A: Use "/dm resetpos". This should make the DM frame visible and put it against the right side of the screen.

Q: What happened to the "Reset Each Combat" option?
A: It was made irrelevant. DamageMeters now keeps in essence two full sets of information: one normal, and one set that applies only to the latest fight. This second set, the Fight set, is what provides the information for the DPS, HPS, DTPS, and HTPS quantities. Those quantities are basically the normal quantities but divided by the duration of the fight. If you turn off the "Visible Quantity\Show Fight Data As Per/Second" option you have what is in essence the same thing as what you had before with the "Reset Each Combat" option.

Q: Why can't DM just automatically sync?
A: v5.1.0 has a BETA auto-sync option. This will sync when you lave combat once every three (3) minutes. In previous versions this was left out for the following reasons: Primarily because sync'ing takes a long time. There is just a lot of data to transmit, and since WoW likes to boot clients that send data too quickly DM transmits it slowly. If you are having problems with frame lag or being disconnected randomly you should disable auto-sync and do it manually after boss fights.