Both are marked "Frontier TEchnologies Corp.
AdCom 2-M Controller", one is
also marked "Version 3" (this one also has a holder for a coin cell on it)
and the other one "Version 5". There's also a Z80-SIO and an 8253 on each
board, and the Version 3 one has an 8255 as well.
Some info at:
http://www.frontiertech.com/aboutus/aboutus.asp