This is a 3.3V Arduino running the 8MHz bootloader, in a very small package - a Mini Arduino, you might say!
You need to wedge an Arduino into a really tiny spot? Simple - just use a SMD '328 IC. Oh... you want a reset, and voltage regulator too? Why didn't you say so!
Try this - the super-flat SparkFun Arduino Pro Mini, featuring a ATMega328 at 8MHz on 3.3V. Mind you, there's no headers and USB interface - you have to wire it up yourself, and have an offboard USB-serial cable to program it with!
Note: Unlike most other Arduino development boards, this one has the USB connection is off board.