Espruino Pico is a tiny USB stick that runs JavaScript code (it doesn’t need to be plugged into a computer). You can program it with nothing but a serial terminal program, but there’s also an IDE that runs in the Chrome Web browser. It’s got a syntax highlighted editor as well as a graphical programming language. Once you’ve uploaded code, you can inspect and change variables (including functions!) while your program is running.There’s loads of documentation, tutorials and support for a huge range of different hardware too.

Specifications

• 33mm x 15mm (1.3 x 0.6 inch)
• 22 GPIO pins : 9 Analogs inputs, 21 PWM, 2 Serial, 3 SPI, 3 I2C
• All GPIO is 5 volt tolerant (Arduino compatible)
• 2 rows of 9 0.1″ pins, with a third 0.05″ row of 8 pins on the end
• On-board USB Type A connector
• Two on-board LEDs and one button.
• STM32F401CDU6 CPU – ARM Cortex M4, 384kb flash, 96kb RAM
• On-board 3.3v 250mA voltage regulator, accepts voltages from 3.5v to 16v
• Current draw in sleep: < 0.05mA – over 2.5 years on a 2500mAh battery
• On-board FET can be used to drive high-current outputs

You can buy it from here: https://www.tindie.com/products/gfwilliams/espruino-pico-unpinned/