Linqdb is nosql database for .Net. It is based on Leveldb and adds some higher-level features, so technically it's just wrapper around Leveldb. It was created with speed and simplicity in mind.
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Linqdb comes as one-process embedded database as well as standalone server with client. The api for both versions is identical.
Leveldb efficiency combined with high-level features like entities, linq-style operators, search and so on.
Linqdb is based on Leveldb which results in great performance characteristics.
Linqdb itself is optimized not to stand in the way.