rollout-features
Initialization​
Add your feature to the rollout_initializers.rb
First argument :slider_overhaul is a feature name, second and further arguments are whatever data you might need, look https://github.com/fetlife/rollout#how-it-works
But don't put any sensitive data there, it will be available on the client side.
this is how it looks on a client side: 
Usage​
Client side: I've added a function isRolloutFeatureActive to powr_helpers.js
Backend: similar to ACTIVE_AB_TESTS, ROLLOUT_FEATURES are added to the globals object
To activate a certain user:​
$rollout.activate_user(:slider_overhaul, User.find_by(email:'[email protected]'))
To activate a feature for everyone:​
$rollout.activate(:slider_overhaul)