I wanted to make device so that I could carry with me. It should be with buttons, screen, autonomous and not completely useless. I decided to write a simple interpreter of the Brainfuck language.
LCD connected to Arduino pro mini via I2C. To digital pins 2, 3, 4 and 5 I connected buttons. Since I do not have any suitable box, I found a big box and put everything in there together with the switch and battery.
The device has four functions: editing the code, executing, saving to EEPROM and loading program from EEPROM. At the moment I have not yet decided where to get data for the operator "," and it just is not executed.
UPDATE: Now you can use operator "," for input!
I'm waiting for your advice or questions. Sorry for my English.