This old board looks strikingly like something that would be featured on Bunnie Huang's "Name That Ware" blog feature (http://www.bunniestudios.com/). I'm going to make a wild-assed guess and say that it's a home alarm system controller. Modem for dialing out. Lots of pins for all the door/window sensors. On the other hand, 24V outputs? That's a weird number. Sprinkler valve controller? It's too high to be some kind of Christmas light controller.