With 2 friends, we have built a "pokemon-go" like platform, called https://geogaming.io, to create fully customisable scavenger hunts.
We sell it mainly in B2B to companies who sell team building events and that need a touch of digital... We have other customer segments coming (zoos, theme parks, tourism offices...)
We also use the platform for individuals,like for birthdays (http://birthdays.geogaming.io) or hens/bucks parties etc.
This platform brings us ~15k a month but it's growing very very fast.
Our architecture is based on AWS lambdas so our infrastructure costs are very limited and the product is highly scalable (games have been played with thousands of players)...