Ever since I started playing around with ESP modules I wanted to measure weather conditions in multiple location at home, friends, etc. The best way to achieve that would be to build a station that gathers various environment parameters and publishes them somewhere. That is what I've done. The very first prototype was done using ESP-1 module, DHT-11 humidity sensor and BMP280 breakout board. The station publishes gathered data to a MQTT broker from where it can be further gathered and analysed.
I was always fascinated with balancing robots and wanted to build one myself. Some time ago I started collecting IMU, arduino boards, wheels, motors for other wheeled robots and one day decided to build a balancing robot instead. I've used wheels from old four wheel drive robot that used mouse sensors for odometry and was driven by an Arduino Pro mini. That robot never went alive anyway :)