Redis and LevelDB are very different, with different use cases.

LevelDB is a key-value storage library that writes to disk. It's the sort of thing you could use as the storage layer for a relational database.

On the other hand, Redis is an in-memory key-value database server.

I've only looked briefly at leveldb, but IIRC redis is _hugely_ more featureful than leveldb (which I'm sure is a great fit where it's used).