Labs hosts a special project called Tool Labs which https://wikitech.wikimedia.org/wiki/Help:FAQ describes as "designed to host tools that are not so complicated that they would require a dedicated instance". One notable tool is Geohack (https://tools.wmflabs.org/geohack/): every article about a location links to it. Example from https://en.wikipedia.org/wiki/Aberdeen:
Coordinates: 
57.1526°N 2.1100°W
57.1526°N 2.1100°WThere are also various analytics dashboards in labs which might be considered as "production"
As others have mentioned, part of the problem is the ease in spinning up a labs instance vs hardware procurement for a deployment into production. Ops (Alex) is working on virtualization infrastructure for use in prod called Ganeti (an alternative to the OpenStack virtualization software which powers labs); the first service was recently migrated from hardware to a Ganeti instance: etherpad. Ganeti could be the way forward for promoting services from labs to prod without requiring dedicated hardware.