J vs MS PowerShell

3 classes of operators (verbs, adverbs, and conjunctions) with verbs the most basic function that take either 1 or 2 (infix) parameters. Operators allow function composition with a minimum of parentheses.

J also supports multiline functional definitions similar to BASIC/Pascal. Including error handling.

Each built in operator is a C/asm function, and special code further optimizes some operator combinations. Result is optimized C speed from quick parsing. Array orientation parses and compiles a function once, and applies it to all array items.

Still actively developed, but most recent changes have been in libraries and IDE and platform support.
Language is considered "perfected"... though not quite.

Complete core programming functional tools allow writting programs and libraries without imports.

(... within each of the 3 operator classes) makes reading code easier. Very simple parsing rules.

The help system is designed to evolve over time; running update-help downloads the latest content.
When searching for help on items, you can simply type help commandname to get information about a command.
If you're not sure what you're looking for, but have a rough idea, you can search on partial command names, or even specify specific verbs to get a list of commands potentially of interest; e.g. help -verb write.
The information in help gives a good overview of the commands you're looking at, along with code examples, so you can see real-world usage without resorting to the web.

When calling a method with multiple parameters, rather than passing one variable per parameter you're able to "splat" one variable to the method, with the parameters taking their values from its properties.

Commands can be chained via the pipeline, allowing output from one to be cleanly fed as input to the next.

PowerShell is installable through Chocolatey.

The language can wrap and interact with code written in other language's, making it highly extensible.

Though Windows Powershell only works on Windows, the open source implementation Pash (http://pash.sourceforge.net/) allows the same language to be run on other OSes.