See http://boinc.berkeley.edu/trac/wiki/PerAppCredit
If enabled (by the <credit_by_app> config flag)
validators will maintain on a per-(app, user, credit type) basis,
and same for teams,
in new DB tables credit_user and credit_team.
This info is displayed in the web site, on user and team pages,
using project-supplied functions to generate the HTML.

Note: update_stats doesn't decay the recent-average values
for per-app credit; I'll add this if needed.