Good sample app for (mobile) user signup workflow?

I am using useraccounts for a while now, but I would like to switch to a another solution. The standard useraccounts workflow may fit to a web application, but it’s not flexible enough to be adapted for a good user experience on mobile devices.

Before I start to develop everything from scratch, it would be great to know about good (open source) sample apps that already built a working user ramp-up process including all the necessary parts like sign-up, sign-in, lost password dialogs etc.

So any hints about existing projects would be highly appreciated. At the moment, I’m using a mix of React and Blaze, so both front-end frameworks would be fine.