I have been looking for an app that will let me keep track of the last time I have completed tasks, instead of scheduling tasks in the future. I ran across a link for an iOS app that is exactly what I was looking for. Apparently, the developer pulled it from the store because he didn't have time to keep up with it. I couldn't find anything like it in the WP Store, so hopefully someone can make one for us.
The basic idea is that you add an event (changed oil in car) which automatically has the current time and date (which can be changed to make it a future or past event) and when you click Save, it adds the event with that date as the last completed date. You build the list like this over time. Next time you "change the oil" you just click that event, and click the Now button to quickly add another completed date to that event.
Link:
Time Flies - Super Simple Event Tracking
Also, I would like to add that I would be willing to pay $2-$4 for an app like this since it is probably niche and not something that everybody HAS to have.