Local-First Strava-Style Social Fitness Tracker Where the Group Lives Without a Cloud Heatmap
Strava has been getting picked apart in 2026 for hoovering 21 categories of data (most not needed to run the app), and journalists keep using its heatmap data to track government officials. Privacy-conscious athletes who still want the social parts (kudos, club leaderboards, route-sharing with friends) are stuck choosing between Strava-the-spy and FitNotes-style local-only solo tools. The gap is a Strava-style social tracker where the social graph is end-to-end encrypted between the people you actually invite, no public heatmap, no firehose for advertisers.
The hard problem is route privacy, not auth. Even if your friend list is E2E, a route polyline starting at your house doxxes you. Build in fuzzing the start/end of every route by N meters by default, and make 'share full polyline' an explicit per-friend choice. That's the differentiator that justifies a switch.
landscape (4 existing solutions)
Either fully local and asocial, or hosted and surveilled. The 'private-by-architecture social fitness app' is a real product hole, and federation/Matrix-shaped solutions haven't been tried in this niche.