I just finished a tiny Leonardo type design that has a few different sensors on board. This one has a RTC, temperature chip, accelerometer, pushbutton and a rotary encoder. It also has the Leonardo bootloader on it which allows it to be pretty small. I'm not sure what it will do since my initial goal was to see if I could get the bootloader into an Atmega. After a few revisions I thought I would fit on as many sensors as possible. All the sensors and display are i2c so routing it was really easy. I'll start on the next one for fix the problems I've found so far. The rotary encoder is way too large so I might replace it with a 5 was navigation switch. The smallest one I've found is 12.5mm square. If you have an idea of what it can be used for then let me know. Maybe a logger of some sort. I'm no good at writing code but managed to get everything barley working last night. The unpopulated bits are the switching power supply. It works but for the weekend I just have it powered by USB to get some code into it. The layout was done in Altium so if you want the files or just the schematic as a pdf then just let me know. It was really fun.