We have used Feathers to build http://www.zeek.ai/ and have been really happy with it so far. The consistency between the client and server libraries makes developing with Feathers fast.
Despite reading that webpage I still have difficulty understanding what the actual product of zeek.ai is. Has it something to do with converting Twitter followers to customers?
I think it's automated following and message sending to Twitter users. Maybe...
Glad to hear you are liking it!
'proprietary' in the Targeting section is misspelled fyi