From the Adafruit Forums: Lira – A Barebones, Low-Cost, Arduino Compatible Atmega328 Breakout Board.

What I came up with is the Lira. It is, as you will see, little more than a breakout board for the ATmega328, but it provides all the bare necessities like voltage regulation, basic power conditioning and an FTDI programming interface. It’s the smallest, simplest, cheapest design I could come up with that still uses through-hole components for ease of construction.

Certainly, your Boarduino has more features, better power conditioning and all of that. But then the Lira is significantly smaller at 2.15×0.85″ (vs. 3.0×0.8″, per the Boarduino page). So perhaps it will find an audience among those in search of the smallest, most bare-bones microcontroller they can build themselves.

Read more about the project on the Adafruit Forums.