Does the Blacknut app support multiplayer?

Yes, Blacknut supports local multiplayer for certain games. An entire section of the library is dedicated to multiplayer games that you can play together on the same screen, in co-op mode or head-to-head.

The icons next to each game let you easily see which games you can play in local multiplayer:

Online multiplayer gaming (playing against users in other locations via the Blacknut app) is currently in development and will be available to play soon.