Imagine union organizers having an app where workers can register anonymously (just wage and location) and help build heat-maps of places where workers are interested in unionizing. This can have increasing returns - see some plant having some interested workers? Send some picketers with download instructions to find the rest.

The app can also provide useful services like to reporting wage theft or other rights violations.

BTW, I'm not even sure trade unions are the right way to solve labor issues, but it is fun to ponder union organizing in the 21st century.