For wifi-connected IoT thing I really like the ESP8266 chip. You can get it in a small form-factor board such as the "Wemos Mini D1" for approximately €3.0. P

For wifi-connected IoT thing I really like the ESP8266 chip. You can get it in a small form-factor board such as the "Wemos Mini D1" for approximately €3.0. Programmable via the arduino-studio, widely-supported, and very reliable. I've built a bunch of projects with them, and couldn't be happier.