Normally I don’t cover apps, but apps for the E-Ink Kindles seem to be pretty thin on the ground lately, and this new one looks really useful.
Metalgrass Software has released the Utility Kit and it is available for the Kindle PaperWhite, Kindle Touch, and Kindle 4. It contains seven different applications: calculator, stopwatch, countdown timer, world clocks, calendar, units conversion, and notepad. The author tells me that it was a year in development. It costs $1.99 and can be bought from Amazon, or you can search for Utility Kit directly in the Kindle store on your device.