It's not the most accurate thermometer in the world, but for this price and the fact that it was homemade...
Step 1: Parts
2x7 segment display
1x1800 ohm resistor
1x KTY-13-5 (temperature sensor)
Step 2: Circuit
Step 3: Software
Step 4: Uses
You can use it in your computer, but you should have plexi glass.
You could also use it for measuring the temperature in a room.
And what about putting it in a greenhouse and monitoring the temperature?
You should just remember that it isn't very accurate.