seeed studio Seeeduino V4.2(ATmega328P), Based on Arduino UNO R3 Bootloader, 100% Compatible with Arduino IDE Project, Single Board Computer Motherboard with 3 Grove Connectors for Widely Application

Bought this for less than $10 shipped with Prime. Great board! Three Grove ports, USB to UART capability (just add a 5 pin header), and 3.3/5 V switchable logic levels. Go to the Seeed wiki for the board and follow the instructions for adding the board to the list of boards in the Ardunio IDE, then start loading sketches. Also really like the micro USB port instead of older mini or type A USB connectors.

I had s 3.3 volt display and all my other Arduinos are 5 volts only, but this one is switchable.

A few things I didn't realize when I purchased this. It already has a few grove ports on it so you don't need a shield for less than 3 sensors. All the power and coms are on a micro USB which is more up to date than some boards.The bad news is compatibility. Their directions for hookup/board selection were wrong--I only got it to work by telling the IDE it was an UNO. As usual with Seeed stuff the directions/software sucks and you're on your own. Not a huge issue with something as common as an Arduino.

Great Arduino clone switchable between 3.3V and 5V operation.

No problems. Worked great.