I'm definitely late to answer here, but a friend and I were fed up of the overcomplicated Java Swing apps, so we built our own open source SQL editor & Database manager. It's 100% Open source - MIT licensed.
It's really modern compared to many of those listed here, but doesn't have as many advanced features, so it is not as well suited for DBAs, but it's GREAT for regular developers.
Hope someone else likes using it as much as I do!