I’m currently working on a affordable Tally system for the Blackmagic Design ATEM Mini (but will also be compatible with other ATEMs).
The Tally system consists of the following:
1. Control unit with Wifi with 4 RJ11 outputs and micro USB as input
2. 4x Camera units with plain old RJ11 connector
3. Software currently running the heavy lifting on a separate computer (Windows, Linux, Mac), looking into integrating all in the control unit.
If you want to help develop this kit reach out to me via the contact form.