Wakoopa is an excellent service which tracks what software you have been running. It keeps tabs of what software is running in the background, what software you have installed, and what software you actively use. Every so often the software uploads this data to the Wakoopa site where it then lists all programs you have been running. The interesting thing here is that you can add friends to track individually or join a team and combine the data. They currently have about 8,000 users.