HSQLDB (HyperSQL DataBase) is a SQL relational database software written in Java. It offers a small, fast multithreaded and transactional database engine with in-memory and disk-based tables and supports embedded and server modes.
The best thing about it was its performance; I compared one of our other databases to this product for comparison purposes - both were running at 100% but when we ran same queries against hypersql they performed much slower than expected by me! This has nothing specific that i dislike as such except perhaps price which might have been better if their pricing model had some flexibility so users didn't pay more per month just because there are multiple instances set up within an account orβ¦
Pros
Excellent support
Relatively easy install process, no special requirements (ease in installing)
Very good documentation with examples included along side them is helpful too.