My first open source project - a REST API wrapper and data synchronization library for Yammer that can be used from .NET applications. Yay!
Check it out: YamrSync
I need it for my Yammer SharePoint Search Integration project (working title: "One Search to Rule Them All"). More info coming soon. Just the basic thought: with the Yammer API limits in place it is not possible to do a full crawl on a Yammer repository on a regular basis. Furthermore we must assume a slow internet connection (remember we need the documents, too). So we basically use MongoDB as a data cache SharePoint will crawl against. And we need the database for storing user permissions our security pre-trimmer will use.