I played a lot with this while evaluating the most of the NoSQL database engines for .NET. I find it very good as it offers a good LINQ support. Indeed RavenDB uses LINQ internally to index the documents. It also supports full-text search based on Lucene engine (lucene.apache.org) and provides high-performance searching.
like most NoSQL databases RavenDB is open-source for OS projects and commercial option is also available.
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Thanks.