HyperLevelDB is a forked LevelDB with some changes, mostly, finer grained locking and changes to how compaction works:

However, it comes with a caveat - one of the changes they made is to take away write throttling if compaction falls behind, the app itself is expected to do that.

Sophia is a competitor to LevelDB. The website claims that in benchmarks it completely smokes LevelDB. I have not explored how it does this or tried to replicate their benchmarks myself:

It's written in C and BSD licensed.

As an example of the kind of speedup they claim to be capable of, they say LevelDB could do 167,476 random reads per second on their SSD based machine. Sophia could do 438,084 reads/sec. Random reads are of course the most interesting for us because that's what UTXO lookups involve.

They also compare against HyperLevelDB, where the differences are much less pronounced and actually HyperLevelDB appears to be able to do random writes faster than Sophia.