I recreated an SQS style service on AWS for sole purpose of avoiding being locked into Amazon. It used their autoscale system and was about the dumbest simplest api you can imagine, just depositing messages into a geographically replicated db table for later processing. We also used it as sort of a backup system, where the messages were never truly deleted and everything could be reprocessed as needed since the front end db that held processed records was an absolute amateur disaster just waiting for some malicious sql injection wipes. It was solid as a rock and extremely low maintenance. I think things have become relatively standardized since then (aka lots of duplicate SQS compatible api/services), so unless there was a serious requirement to stay off SQS I'm not sure I'd do it again.