AFAIK the single user version of CALCIUM is free.

http://www.brownbearsw.com/calcium/FeaturesList.html

This is a really good calendar with tons of features. Never had any problems since we installed it three years ago. It has one of the best install programs I have ever seen, installation was a real breeze. Whats more, the people at Brown Bear Software are really helpful if you need some special coding.


HTH,
Alex