twzERD - online entity relationship diagrams
twzERD is an online tool for creating simple database entity relationship diagrams (ERD). It's suitable for small databases of less than about 20 tables (more with a higher screen resolution). Here's an example of the kind of thing I'm talking about:
This project was started as a fun little exercise for myself, and was never going to be made public - but here it is. It's fairly restrictive in what it can do, and is certainly no match for proper drawing or charting applications. But if your requirements are simple (which many of my custom databases are) then twzERD might be of use to you.
Note that twzERD uses the HTML5 <canvas> element; it should work with Firefox, Safari, Opera, Chrome and recent versions of Internet Explorer.
For more information and to try it out, go to twzERD online.