Basically, this guy set out to write a really small (or smallest) Turing complete language back when the Amiga was king. Apparently, he got it down to under 200k.

Here is the full list of commands.

• >  Increment the pointer.
• <  Decrement the pointer.
• +  Increment the byte at the pointer.
• -  Decrement the byte at the pointer.
• .  Output the byte at the pointer.
• ,  Input a byte and store it in the byte at the pointer.
• [  Jump forward past the matching ] if the byte at the pointer is zero.
• ]  Jump backward to the matching [ unless the byte at the pointer is zero.

To really appreciate this, you have to check out the examples here and here