Dual-track agile
Dual-track agile (sometimes called dual-track discovery and delivery) is a product-development model, codified by Marty Cagan and Jeff Patton, that runs two parallel workstreams: a discovery track that validates which problems are worth solving and what solutions will work, and a delivery track that builds the validated solutions.
The model exists to fix the failure mode of single-track agile: engineers build whatever the backlog says, the team ships features that don't move the metric, then everyone wonders why retention didn't change. Discovery in dual-track is continuous, user research, prototype testing, opportunity-solution trees, not a one-time 'requirements phase'. Delivery is normal sprint-based execution but only against opportunities that discovery has validated. The model assumes a product trio with real authority; it fails in organisations where 'discovery' is a checkbox before a pre-decided feature gets built. Pairs naturally with continuous discovery practices (Teresa Torres) and opportunity-solution trees.