LuMongo is a real-time distributed search and storage system based on Lucene. LuMongo is designed from the ground up to scale both vertically and horizontally across servers. LuMongo stores Lucene indexes directly into MongoDB. Documents can be stored natively into MongoDB. When stored natively document can be queried as normal out of MongoDB and use of Map-Reduce and the Aggregation Framework is possible.
To learn more see the wiki: