tinyBF is a brainfuck equivalent with only 4 characters. It's a variant of RISBF and was created by Michael Gianfreda, Nov. 6, 2014. tinyBF programs are smaller than RISBF's. The motivation for creating tinyBF was to have four 2-bit commands in one byte of program memory.
||Switch direction (- <-> +) (default: +)|
||Change data in selected direction. BF equivalents: |
||Change cell in selected direction. BF equivalents: |
||Jump in selected direction. BF equivalents: |
Since switching the direction twice doesn't change anything, we can use this as the output function: ==
The brainfuck endless loop  can be used as input function: |=| if switch is positive, =|=| if switch is negative.