We've written a GUI application. Its command-line options are like those in the mysql client. Its graphic features are an SQL-statement text editor and a scrollable SQL result set. It runs on Linux now and we believe it could be ported to other platforms.
Here are four screenshots.
The startup is as non-GUI as can be -- in fact it gets options from the command line, or from my.cnf, the same way that the mysql client does. Wherever it seemed reasonable, we asked: What would mysql do?