Tideline — Local-first todos with realtime collab.

The problem

Couples and small teams have one specific shared-list need that no app handles well: a grocery list, a packing list, a household-chores list — something both people edit, that should sync in real-time, that should work without internet (you're already at the grocery store and lost signal), and that shouldn't feel like deploying enterprise software. Notion is overkill. Things doesn't sync between accounts. Apple Reminders is fine but its sharing UX is grim. We can do better with a focused product.

Our approach

Tideline is local-first (CRDTs under the hood) so edits work offline and merge cleanly when you reconnect. Sharing is one-link: paste a Tideline list link into iMessage, the other person taps, they're editing it on their phone in <5 seconds. No accounts required for the receiver to view + edit. Pricing is $4/mo per editor, lifetime free for view-only. Native iOS + macOS first, web sync built on the same engine.

Where we are

TestFlight beta with 67 users for 4 weeks. 78% weekly retention (median across cohorts), highest engagement is the "shared with partner" cohort at 92% weekly. NPS 64. Zero churn so far at week-4 (small N, but indicative).

Where we're going

The shared-list primitive done right, and a thoughtful payoff for local-first as a UX choice (not just a tech choice). Long-term: a primitives layer for any small-group shared-state app — wedding planning, road-trip itineraries, tabletop campaign notes. The engine is the moat; the todo app is the wedge.