Counting currently "hot" applications

To make a dynamic listing of applications that are "hot right now", we need to store some additional download statistics per application:

Total amount of downloads
Average downloads per day during last week
Yesterday's downloads
These can then be used to calculate whether an application is getting more downloads on a given day than usual, meaning that it is "currently hot".

This should be possible to count via:

current karma = (yesterday's karma - age modifier) + (total download count - yesterdays downloadcount - lastweeks daily average)

Source.