Credit card expenditure: since my old-school bank has no API of sort, I trigger via Tasker a daily sms to a bank number that replies with the amount left before I get to my CC limit. I then parse the sms (Tasker again, using JS) and display the amount that I have spent so far on the home of my mobile. This simple warning has dramatically helped me to keep my CC expenditure in check.

Goodreads yearly target: using a combination of Tasker, Goodreads API and some JS, I display the amount of pages I have to read each day in order to reach my yearly target of books (assuming an average length of a book of 250 pages).