YACL is a typical damage meter that puts focus on analytic details. You want to know how much crushing blows your tank is eating ? Need to now details about who is healing most efficiently ? Then YACL is for you. It was build by the author to optimize his spell rotations.
And best of all - YACL works just fine with WoW Classic.
Don't worry about the message that says it is outdated, it is not. It is from the future :)
In the past, YACL used to be a synchronized damage meter. That feature has been removed, Sorry.