Diameter is a lightweight DPS meter for World of Warcraft retail.

Version 2.4.0 is here with a more explanatory header text.

You can navigate between Modes, Group and Breakdown using right and left clicks.
Multiple windows support. On version v2.3.0, with 4 windows it was using 210 KB of memory and 0.3% CPU during a dungeon run.
You can look at your spell breakdown at all times; if you want to look at your most damaging spells or someone's healing spells or the tank damage taken, Diameter got you.
You can see the breakdown of other players during combat: by clicking on a player you will be prompted to select the player from a second list and then you can see the breakdown. This is due to a Blizzard restriction on their API.
It's written from scratch with Blizzard's new C_DamageMeter API in mind, so no legacy code with CLEU parsing.

It is inspired by an addon called Skada.

Code is hosted on Github.

Known issues:

There's a lot of UI improvement to do still, check the roadmap on TODO.md.
If you look at someone's breakdown after combat ends and a new combat start, you can keep looking at the spell breakdown of that player. I don't really know if this is a feature or a bug, but it happens because the game drops the secret value of the player.
You can't see the breakdown of other group members straight from the combat data while in combat due to Blizzard's restrictions, but the addon will navigate you to Player Selection Mode to circumvent this. You can see others' breakdown after combat ends without going through Player Selection Mode.