What addon is this?
 

The one that lists what recipes use the mat. It's a rather lengthy list for things like leather, and was wondering what it is?

Unless I am mistaken, that's Mendeleev

What is that "Used for: Engineering, Leatherworking, Tailoring, Blacksmithing" shown in WoW's normal tooltip? Is it part of the whole Auctioneer AddOn? Or is it some other stand-alone addon?

Gemini_II answered that question. To repeat it is Mendeleev.

Not to open new thread like this. What addon is this?

Probably Grid

The long "component in" or "used in" list can be turned off in Mendeleev's options. Yep, that's Grid.

Mendeleev may do the same thing (or something similar), but that piece is quite clearly coming from Informant (part of the Auctioneer package).

Thanks for the replies :)

The Component In, Gathered By, Crafted By, etc. in the main tooltip is from Mendeleev, and the info "Used For:" in the Auctioneer toolip added underneath is from Informant, yes. :)