Webhook Service Provider or Project

Does anyone know of a service provider or a project that will provide me with webhook functionality? Sure it's just a matter of sending a HTTP/S POST, but it should be implemented with a queue for durability and also some sort of retry logic. I'd prefer not to implement this if there is a project, package, or service that provides this.

I did find pubsubhubbub but that's just a reference application and protocol specification. A production implementation of this would be great if it were available.

Amazon's SNS allows both http and https, email, etc

I know this post is old, but www.inflectus.com provides a managed webhook service.

Disclaimer - I am involved with the company