Arduino and Arduino compatible dev boards are an awesome tool for developing an idea quickly but, being development boards, they're often a little more bulky and full featured than you really need. Having a USB interface and a bootloader is so nice, though, so we put together the bare minimum Arduino compatible breakout for integration into your small projects. We call it the Atto84.
The Atto84 is essentially a breakout board for the absolutely minute WQFN ATtiny84, but we've done some work to make it easier to program. First off, we've added a micro-USB connector and a firmware-based USB driver for the ATtiny that allows you to program the chip over USB. In addition, we've created an Arduino board profile that combines this bootloader with an extremely full-featured ATtiny Arduino core.
Simply install the USB drivers on your computer, select the board profile from Arduino's Board Manager and upload code to this board like any other Arduino style development board.
There are very tiny silkscreen pin labels on the top of the board (which correspond to the Arduino pin numbers, not the IC pin numbers) and larger labels on the bottom side of the board. A reset button allows you to put the board into bootloader mode for programming and an on-board LED attached to pin 8 makes for a handy status indicator for your project. Thin pcb construction and castellated headers make the Atto84 very low-profile but the addition of 0.1" pin headers turns it into a handy, breadboard-friendly, package.