In goal settings we’ll have a field similar to Supporters where you can add collaborators who will ALL BE CHARGED along with you if the goal derails. We email the collaborators a link to opt in and then the goal appears in everyone’s goal galleries and any of you can add data. Everyone set their reminder settings individually (but initially we’d just have shared reminder settings so the group members would have to coordinate on that — the settings page could throw up a banner warning about it). Or maybe it’s not that hard for each person to set their own reminders independently even though they reference the same goal.
The meta data shown in the mouseover for the datapoint should include the username. Users may want to use a convention of signing datapoints in the comments so it’s more immediately clear who added what, but we can ship this without imposing any structure on that.
Uluc proposes just sponsored goals where you can create a goal for a friend but you get charged.
Step 0 should probably be just a way to have other people’s goals in your gallery.
See also thread with Giles Edkins (@gdedkins) about “reverse beeminder situation, where you have to complete a particular task or someone else gets fined”. I was thinking we could have the best of all worlds here if you could just choose the subset of people on the group goal who get charged on derailments. Then you could make a goal for a friend where you’re the one who gets charged and not them. (Lots of details to worry about here, like the “Beeminder can’t be a credible threat” banner.)