Pro Trinket combines the common core Arduino chip, the ATmega328. It's like an Arduino Pro Mini with more pins and USB.
Sometimes you just need more pins, more FLASH, and more RAM. That's why we sel the Pro Trinket, with 18 GPIO, 2 extra analog inputs, 28K of flash, and 2K of RAM.
It has onboard USB bootloading support, MicroUSB jack and Optiboot support.
The Pro Trinket 5V uses the Atmega328P chip, which is the same core chip in the Arduino UNO at the same speed and voltage. The Pro Trinket is programmable using the Arduino IDE and 99% of Arduino projects will work.
Specifications:
ATmega328P onboad chip in QFN package
16MHz clock rate, 28K FLASH available
USB bootloader with a nice LED indicator looks just like a USBtinyISP so you can program it with AVRdude and/or the Arduino IDE with a few simple config modifications.
Also has headers for an FTDI port for reprogramming
Micro-USB jack for power and/or USB uploading, you can put it in a box or tape it up and use any USB cable for when you want to reprogram.
On-board 5.0V 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
On-board green power LED and red pin #13 LED
Reset button for entering the bootloader or restarting the program.
Works with 99% of existing Arduino sketches (anything that doesn't use more than 28K, and doesn't require pins #2 and #7)
Note
The Pro Trinket USB technique it uses doesn't work as well with modern computers. So while we still carry the Pro Trinket so that people can maintain some older projets, we no longer recommend it.