Firebird, and by extension the industry specific application which utilizes it.
This applications is absolutely usability nightmare, created in 90s, and it hadn't undergone any change since then. It's database design is also absolutely horrible.. yet it is faster, and more comfortable to just use plain SQL to work with it than bother with UI.
Then there is that piece of shit known as firebird. It has all downsides of file based databases, while also having all downsides of service based databases.
It also has its own way of doing things, and it doesn't even have services/systemctl service by default. Prior to version 2.5 you couldn't drop connections, and guess what - that PoS application set it to a week.
File itself wont update if there is any live connection.
That piece of shit app uses legacy client dll for firebird, so you can either connect to firebird 3, or to firebird 1/2. but not both.
And then there is firebird documentation, which is horrible, and fragmented.
I could rewrite that piece of shit, and design a better database but we won't ever compete with that company for political reasons.