Built a last-mile delivery/logistics management system to power deliveries for on-demand/hyperlocal services and launched it last year (mentioned it in another one of these threads last year)
To date it's handled more than 70k orders, ingested nearly 10m telemetry records, has been extremely reliable, is almost entirely self-contained (including the routing stack so no expensive mapping dependencies) and is very efficient on system resources.
It handles everything from real-time driver tracking, public order tracking links, finding suitable drivers for orders, batch push notifications for automatic order assignment, etc.