CruxPA is a hybrid program which doesn't really fit into any one category.
The best way to describe it is as an online system to store details of appointments, tasks, telephone messages and customers
It is extremely easy to use and also very light on resources (just 2Mb installed!)
For organisations with more than one person, it also has the ability of leaving messages, tasks and appointments for other people, tracking their status and editing/deleting them once submitted
For privacy, contacts can be stored as either personal or global
As with all Crux software, CruxPA is a free download, released under the GNU/GPL License
There is also an online demo available here