Right now I’m using the APIs of beeminder and activity watch to link the two together. It’s just a infinite loop with a sleep delay. It would be nice to make it more official though, and compete with Rescuetime in this space.
Most beeminder users who try to use Beeminder to manage their use of devices will see Rescuetime as a suggestion, and never hear about nor have the technical know-how to use ActivityWatch instead, which I think is a shame.