MySQL Workbench runs on Windows and Linux. The commercial version will let you reverse engineer and edit the stucture of a live database, with the free one you have first to dump the structure to a file. Its ancestor DBDesigner is a bit older, but doesn't have this limitation. Windows and Linux too.
If these two are overkill you may try with HeidiSQL, the descendant of MySQLFront. It runs on Windows only, but there is an alpha version running on Java.