While developing Vigil we ran into a problem. Having two developers and trying to maintain our build numbers. There were various scripts out there that took the current number and incremented by 1 or used your git SHA. Both of those have different issues associated with them. Just incrementing by 1 causes collisions with the other developer. The git sha is not sequential and causes issues with uploading to iTunes Connect or other app delivery systems such as TestFlight or Hockey.
So we created BLDNMBR.com.
BLDNMBR.com is an open source solution to the problem. It is a node.js server that gives you the next build number through an http request.
Vigil is providing an instance of this service free for anyone who wants to use it. If you would rather run one yourself, you just need a node server and a redis server.