Burro
From Esolang
Burro is Brainfuck-like language, the set of whose programs form an algebraic group under the operation of concatenation and over the equivalence relation "computes the same function". Burro was designed by Chris Pressey between 2005 and 2007.
The fact that Burro programs form an algebraic group means that every program has an inverse that, when concatenated with it, results in a nop. This is a form of reversible computing.
