I've wanted to start playing with them but haven't had the time. MPJA & MCM Electronics sell both Arduino and Raspberry Pi. I guess the Basic Stamp boards came along many years earlier. For some reason, they like to call the boards, "shields". I would check out those three families and you will probably find a few more out there. Right now, I'm using Microchip's PIC10F202 to switch nav and landing lights for R/C planes. An 8-bit Flash uC in a 6 or 8 pin package. Amazing stuff! Have fun!