DrawPlus4

Serif Software make earlier versions of their products available for free on their freeserifsoftware.com website and one of the best is Drawplus4

You can draw almost any shape and edit the shapes 'nodes' that makes it up. You can also 'envelope' shapes and text and there are extensive built in shapes such as clock faces, spirals and others. The program allows you to apply transparency to any shape and text and also imports pictures such as photographs and later the colour and texture. You can draw a shape and drag a new colour onto it to change it and any transparency and lines will take on the new colours

A killer feature is that the drawings can be exported in.wmf format and imported into techsoft 2D designer and other educational programs

A note of caution, the software can be a little unstable as it is basically win98 software and the latest version 7.0 is undeniably better. Save often and try not to run at the same time as other critical work. This seems to be due to a long standing bug in XP relating to drawing circles but is annoying

Try to avoid registering with Serif a sthey can hassle you to upgrade, thoguh its worth upgrading if you can negotiate a low price

Here is an example of transparency in action