Joakim made a coundown clock for his wife and documented the whole process on his blog:
The clock is built using an Arduino, and has a battery powered real time clock to remember the time while powered off.
To make it truly stand alone I added the possibility to set the time and time-to-leave using buttons.
The clock was built into a custom made plexiglass box, and the outside covered with a design printed onto photo paper with a sticky back side. I used my wife’s Cameo vinyl cutter printer to cut the paper – I just love that machine!
Project info at A to Synth blog.