I was just looking at options for push notifications in ruby. I found a gem called apn_on_rails (https://github.com/PRX/apn_on_rails) which sort of worked. But I didn't know how to keep persistent connections and was afraid of accidentally spamming Apple's servers. I thought about outsource the problem to Urban Airship, but unfortunately their free service only works for 45 days then costs hundreds of dollars a month. Grocer looks really interesting and I'd definitely want to try it out.