Adders

Adders is a esolang with only one accumulator (but infinite variables) that uses code as variables to work

Commands:

+ add 1 to the accumulator 
- subtract 1 from the accumulator
@: Loop until accumulator is zero
 ...
x = ... redefine or define x
$(x) print x
# set accumulator to user's choice
? add 1 or -1 to the accumulator (50% chance)
\ escape character 
\x the accumulator's value
[x] code x

Programs:

Looping counter

+
* = $("\n")
@:
 * = $("*")[*]
 [*]

Truth machine

#
$("\x")
@:
 $("1")

Cat program

@:
 #$("\x")

XKCD

++++$("\x")