Depending what "data use" means here, if you mean "bandwidth / traffic use per application", you might want to have a look into this one:

http://thpinfo.com/2010/bwmon/

(We did some research to base that app on, and did not find something that's comparable to what we do - measuring per-application bandwidth without modifying the applications themselves. The bandwidth is calculated out of the time and traffic, so you can measure traffic/data use with it, too.)