The Blackmagic Design GPI & Tally Interface box for ATEM provides 8-pin input/output connectors for connection to ATEM mixers and Videohub routers. Tallies will be displayed when connected to an ATEM mixer to indicate "on-air" status, and it's even possible to connect several interfaces together to increase the total number of inputs and outputs.
The GPI & Tally interface also functions as a Videohub control panel without buttons and LEDs, so you can use your own!