Uhm shouldn't that be ovious by reading the high level descriptions of each? They are for completely different use cases. Membase is a distributed Key/Value server and LevelDB is a Key/Value library.

I see the difference between a server and a library, but both can often be used for the same use case. Just recently I evaluated a few data stores for a project and I didn't care all that much about the distinction. For the servers you're gonna use an API for your programming language anyway, so the programming model isn't that different.

About like the difference between mysql and sqlite.