Om is an experimental, unique take on concatenative languages that attempts to be the simplest language possible (and not simpler).
Defining features of Om include:
Extremely minimal syntax. Each program consists of only three syntactic elements: operand, operator, and separator.
Prefix notation rather than postfix. Rather than passing a data stack to each function, the remainder of the program is passed to each function for rewriting.
A unique "panmorphic" type system in which there is only one data type exposed in the language (a program), even though the implementation can optimize data representations for operations.
Unicode compliant and implemented using C++, Boost, and ICU.