SQLicity is a single file web application written in PHP by Chris Rogus to manage MySQL databases.
Chris has been using this in production since 2005 but has been lazy about releasing it to the public before now.
It offers only a purely text based interface designed to manage the database in an almost exactly 1:1 relation to the actual mysql commands that manipulate the db as if you were using the mysql command line client. In short, it is meant really just for power users who want a decent visualization of their data, and easy access to modify little bits here and there, without the bells and whistles of other db management applications that are aimed at the nontechnical db admin with all the hand holding that such things entail.
In short, SQLicity is meant for those who already know what they are doing!
If you consider yourself such a person, or are willing to take the risks of learning the hard way... Download SQLicity
Note: "SQLicity" is pronounced "skwu-li-city"
Install instructions: download the zip file, extract sqlicity.php, then upload that to a web server with php 4+ and mysql 4.0+, including any shared hosting sites as far as I can imagine (the only problem then might be access to the db's processlist), where you know your db username and password. Open sqlicity.php in your browser, enter your db username and password as the basic HTTP authentication. You are then able to manage your db in the browser, voila.
For the record, no, basic http authentication is far from the most secure way to handle such things. This is meant to be quick and dirty so if you want something more elaborate, feel free to integrate it with any db+cookie based authentication scheme you have on your website, it will be very easy to make that transition: just pull the $sqlicity_username and _password from your state tracking db instead of from $_SERVER's PHP_AUTH_USER and PHP_AUTH_PW, and change show_auth_box() to redirect to your own login page instead of serving an HTTP authentication box request.
2008-08-08: 2008080802 - the first public release of sqlicity is offered.