calendar tools and other productivity software

Finding just the right calendar/"issue tracker"/"workflow manager" seems tricky. Here are some things I've noticed so far:

• trac looks a little heavy-duty for our needs, but has some good attributes
• http://www.taskjuggler.org/docs.php for Gantt charts and more
• really simple, but maybe too simple http://www.eecs.umich.edu/~pelzlpj/wyrd/ (but comes with a great Flash demo!) It's neat to see/show what can be done with simple tools.