I don't have a side project to recruit for right now, but I've wanted this very thread in the past. My current projects all revolve around reducing my dependency on commercial SaaS products. A hypothetical project I'd be interested in contributing to would be an ActivityPub Strava/Ride with GPS clone.
I like the goal of reducing dependency on SaaS product. I use these Strava/Garmin apps a lot and while Strava was cool for a while it hasn’t progressed and doesn’t feel worth the money. Curious to hear what you had in mind, I am in the geospatial space and work with routing tools, etc.
I don’t have a feature list off the top of my head. The basics that Strava offers would be a good start: show your GPS tracks on a map, allow sharing with friends, a chronological feed of your friends’ rides.