An Adafruit Trinket powered TogglDesktop start/stop button
This allows an Adafruit Trinket USB device to send the "Ctrl+F8" key combination to Windows, where the TogglDesktop timer app listens for it and starts/stops the running timer.
It also has the NeoPixel library, but doesn't really do anything with it yet (v2.0 will use a Pro Trinket with enough memory to handle complex LED animations).
Requires the TrinketHidCombo library from Adafruit.
More info: http://www.atomix.com.au/2015/01/creating-toggldesktop-startstop-button/