AVR is a family of
RISC microcontrollers from
Atmel. Unlike the
PIC, the AVR
instruction set is compatible across models. The AVR was designed for efficient execution of
compiled C code. Thus some instructions, such as add immediate, are strangely missing (you have to subtract immediate the complement instead) and others, such as compare with carry, are included.
Like the PIC, it has a dedicated hobbyist following (exemplified by the "AVRFreaks" forum), largely due to the existence of cheap/free development tools.