LeafLabs Maple

So I'm a little late to the party on this one (read:  an entire year), but there's another open-source microcontroller available to the discerning DIYer that is compatible with all the Arduino add-ons (called "shields" in the 'biz).

The Maple by LeafLabs (licensed under Creative Commons) is distinct enough from the Arduino platform to deserve its own place in the microcontroller world.  Perhaps the first difference people will notice is that it's much, much, MUCH faster.  Tests by Make:Zine's staff put the update speed of the digital/analog converter, the component responsible for reading sensors and passing information to the processing unit, at 9x that of the Arduino Duemilanove.  This further opens the applications of the Maple to things like live audio editing, real-time GPS processing, and really anything that requires more bandwidth than you might want to squeeze out of your Arduino.

Found on Make:Zine's website, www.makezine.com

Because the Maple is built off of an ARM processor, you can expect the instruction set to be compatible with similar hardware.  This actually makes the Maple more palatable to "serious" microcontroller programmers, or those who scoff at the Arduino's slow speed and proprietary programming interface.  This also means that if the Maple were to go off the market, or if, say, you wanted to homebrew your own chip for this board, you could more easily find a drop-in replacement already available on the market, without needing to fabricate your own.

Unfortunately, the Maple has two major downsides.  First, the processor is smaller than the Arduino and is attached directly to the board with solder, meaning you can't simply replace it, even if you did find a suitable replacement as detailed above.  This makes mixing and matching impossible, and limits the ability to use the Maple as a prototyper (which, arguably, it is not, unlike the Arduino, which was created with this purpose explicitly in mind).  Second, there is not yet a large community of enthused users surrounding the Maple.  Perhaps there will be in time, as it is adopted and trickles out into the world, but a year in production is not very long considering this is an open-source, editable product.  Not having used one i cannot say for sure, but I can be relatively certain not all the bugs are worked out.

Nevertheless, the Maple is a very capable device.  And, as mentioned at the beginning, it is entirely compatible with the Arduino shields and add-ons.  If your project requires more bandwidth or more power, definitely consider picking one of these up.

Some links of interest:

Maple Documentation

Maple Distributors

Maple Licensing