iOS: It sucks when an appliance breaks and then you find out the warranty has expired. Stuffcard tracks your purchases along with your warranties, and reminds you when they end.
When you get a new computer or other gadget, that's the best time to record your serial number and warranty. If you don't have a good system already, Stuffcard does it all. Scan the barcode of the product and Stuffcard will figure out what it is. Put in the warranty expiry date and the app reminds you right before it expires. That model information is handy when you need spare parts or a replacement ink cartridge, too.
Remember that your consumers rights are stronger than any company warranty -- if something expensive breaks down, you should seek a repair even if the warranty itself has expired.
Stuffcard [iTunes App Store]