I recently picked up a Propeller Board of Education from my recent trip to Parallax, Inc to teach the Teachers' Institute for the ARRL. The Propeller is Parallax's latest microcontroller platform that offers far more than the old beloved BASIC Stamp could. Digging back through my old posts, I found my initial review of the Parllax BASIC Stamp from 2006. (Little did I know that about 5 years later I'd begin teaching classes on the Stamp, visit Parallax HQ, and befriend the author of the "What's a Microcontroller" book (among other titles).)
The Propeller is a programmable multicore microcontroller that can be programmed in Assembly, Spin (an Object-Based programming language that I'm still learning), or, most recently, Standard C. The multicore design lends itself well for many, many projects, chief among them is robotics. Now your creations can take in and process loads more data at once. And with robotics, the more sensory input your bot has, the better equipped it will be to handle various tasks.
I just recently began to fully grasp the power of the little Propeller chip. Once the relative simplicity of utilizing the 8 cores available (known as "cogs"), the possibilities begin to multiply and compound one atop the other. My initial reluctance to the Propeller was the Spin language. The operators seem a bit foreign compared to the C-style languages I've been comfortable with for so long. The various code sections also seemed confusing initially. After reading through the tutorials posted on the learn.parallax.com website, I was up and running in a relatively short amount of time. I also took advantage of the Propeller Manual (pdf) and Programming the Propeller with Spin (pdf). While both offer great starting points, be sure to reference the learn.parallax.com site first - the Programming the Propeller text has its weaknesses. All in all, Spin is a relatively easy language to pick up if you already have some programming under your belt.
Another great aspect of Spin is the ability to utilize Spin objects (or libraries) from the Propeller Object Exchange. Modern microcontroller programming is all about code reuse and sharing: find the code you need that someone else (hopefully) did a good job writing, plug it into your codebase and immediately make use of it.
Far more exciting still is the recent ability to program the Propeller in C. While Spin is great, having to learn another language can be a real turn-off to would be programmers of such a chip. The Arduino is neat in that regard and I must admit I've been smitten with the Arduino since beginning its use. However, the Arduino can only do so much. It is limited by the fact that it's a single core design. For the past few years, users have sacrificed power and utility in order to gain ease of use - no more. With the upcoming release of the stamplib C library, there's little reason to not opt for the Propeller.
Oh, what's that? Price is a big selling point? The Arduino typically sells for $30, the Propeller Quickstart sells for $25 ($50 if you want it from Radio Shack today and can't wait a few days for UPS).
The PropBOE is far more extensible, though. It currently has a high price tag but comes with a lot to offer. VGA output, 1/8" audio out, microphone for audio in, micro SD for storage, ADC and DAC, a mount for an XBee wireless module as well as the ever-present bank of LEDs for feedback - did I mention is has tie points for 6 servos? Not bad for $130. If that seems a bit too steep and you doubt you'd use all the features, a stripped down PropBOE is rumored to be in the works for a target price of $50.