There are many so-called 'Arduino compatible' platforms on the market. The ESP8266 – in the form of the Wemos D1 Mini Pro – is one that really stands out. This device includes WiFi Internet access and the option of a flash file system using up to 16 MB of external flash memory. Furthermore, there are ample in/output pins (though only one analogue input), PWM, I²C, and one-wire. Needless to say, you are easily able to construct many small IoT devices!