Good when you want a lower-power and lower-voltage setup
Same core chip in the Arduino UNO/Duemilanove/Mini/etc
Programmable using the Arduino IDE
95% of Arduino projects will work out of the box
Trinket's got a big sister in town - the Pro Trinket 3V! Pro Trinket combines everything you love about Trinket with the familiarity of the core Arduino chip, the ATmega328. It's like an Arduino Pro Mini with more pins and USB tossed in. But sometimes you just need more pins, more FLASH, and more RAM. That's why the Pro Trinket has 18 GPIO, 2 extra analog inputs, 28K of flash, and 2K of RAM. Like the Trinket, it has onboard USB bootloading support - with MicroUSB jack this time. We also added Optiboot support, so you can either program your Pro Trinket over USB or with a FTDI cable just like the Pro Mini and friends. The Pro Trinket PCB measures only 1.5" x 0.7" x 0.2" (without headers) but packs the same capability as an Arduino UNO. So it's great once you've finished up a prototype on an official Arduino UNO and want to make the project smaller.
Item Specifics ATmega328P onboard chip in QFN package running at 3.3V logic 12MHz clock rate, 28K FLASH available USB bootloader Headers for an FTDI port for reprogramming Micro-USB jack On-board 3.3V power regulator with 150mA output capability and ultra-low dropout. Up to 16V input, reverse-polarity protection, thermal and current-limit protection. Power with either USB or external output (such as a battery) - it'll automatically switch over Size: 38mm x 18mm x 2mm / 1.5" x 0.7" x 0.08" Height with MicroUSB: 4mm / 0.16" Weight: 2.6g