I'm starting this thread as a place to talk about fab-able arduino alternatives.
I'm learning how to use the Modela for making circuit boards using one alternative (see this thread). The problems with the Fabio board discussed there are:
1) 3.3V supply - this appears to be because they are running the power from the FTDI cable through a regulator. But the FTDI cable gives regulated power. Using 3.3V vs. 5V means that your board is not the same as the "standard" arduino in terms of output logic level.
2) Not all I/Os exposed - the Fabio has significantly less I/Os than a standard Arduino (e.g., the Duemilenove). This appears to be to keep the size of the board down and make routing easier.
3) Pads not in the standard "shield" pattern. Also, the pads are not sized such that you can use female headers (or really, any headers without some gymnastics).
I've started designing a fab-able arduino with the following attributes:
1) Uses the FTDI cable for programming (I'd like to change this to using V-USB and a separate ATtiny for USB control, for instance like the Metaboard);
2) Same I/Os and pin layout as the Duemilenove;
3) Single-sided, no through-hole, no jumpers (other than 0-ohm resistors);
4) Constructable in a fablab using 1/64" router bits and (as far as possible) parts from the standard fab lab inventory list.
I started with the Eagle schematics and board layout for the Arduino Pro. I still need to convert the connectors to SMD footprints, but my current progress is here (schematic, board). I'm going to set it up to use the standard female sockets (6-pin and 8-pin), and SMD versions of the pin headers for the ICSP (double-row breakaway) and FTDI cables (single-row breakaway).
I'm not an expert, but maybe you can have a look at the Ottantotto.
I did have a look. Great effort buddy!