Seriously

Seriously is a golfing language created by Mego in 2015 and still under development. It is a stack-based language with overloaded single-byte command names. In addition to the stack it has 2 named registers and an indexable permanent array. Its creation was inspired by this thread on PPCG and is being developed to be used in code golf challenges on PPCG.

Commands
The following are the currently implemented commands in Seriously (as viewed in CP437 encoding). When possible, the character at each code point is listed in parentheses following the ordinal. For non-printing characters (ordinals 0-31), this is not possible, so a description is provided instead. All bytecodes except for 00 will be implemented eventually. Commands are often described in terms of Python functions.

There are 4 data types in Seriously: numeric, string, list, and function. a represents any value. This usually means numeric values, but can represent any value of a type not specified in an alternate command definition. "a" represents a string value. [a] represents a list value (in most cases, a string value is also acceptable). z represents a complex value. Complex values are a proper subset of numeric values. f represents a function value.

Some commands have fixed arity. Others have variable arity. This is denoted by the number of values listed in the pop. Those commands that are not functional commands (such as delimiters) do not have arities, and so do not pop from the stack.

The functional commands each operate differently based on the data types of the values popped from the stack. In some cases, that order matters. In others, it does not. Each operation will be denoted by the different data types popped. If there is a conflict, the most restrictive applicable definition is used.

Hello, World!
H or "Hello, World!"

Primality Test
,p

99 Bottles
N

Coprimality Test
,,┤

Counting the divisors of a number
,w`iXu`Mπ

Truth-machine
,W■

Implementation
In Python on Github

On the web: Try It Online