RavenDB:
- It has Lucene built-in for your full-text searches.
- It can be replicated.
- It supports sharding.
- It has a HTTP API so you can in principle use it from any platform.
Cons: it’s AGPL licensed. Depending on your dev/server environment, you could consider it running on .NET a con. Also I’m not aware of the status of clients for other plaforms than .NET.
Solandra:
- Integrates Solr and Cassandra
- Full-text search managed by Solr
- Replication and sharding managed by Cassandra
Cons: not yet released.
ElasticSearch:
- It has Lucene built-in for your full-text searches.
- It can be replicated.
- It supports sharding.
- It has a HTTP API so you can in principle use it from any platform.
ElasticSearch looks similar to RavenDB but it seems to emphasize full-text search where RavenDB emphasizes being a general NoSQL database.