Nim is a systems and applications programming language. Statically typed and compiled, it provides unparalleled performance in an elegant package.

   High-performance garbage-collected language
   Compiles to C, C++ or JavaScript
   Produces dependency-free binaries
   Runs on Windows, macOS, Linux, and more

Simulation of the Apollo Guidance Computer (AGC) and its display/keyboard (DSKY).

dygraphs is a fast, flexible open source JavaScript charting library.

KaTeX is a fast, easy-to-use JavaScript library for TeX math rendering on the web.

Fast: KaTeX renders its math synchronously and doesn't need to reflow the page. See how it compares to a competitor in this speed test.
Print quality: KaTeX’s layout is based on Donald Knuth’s TeX, the gold standard for math typesetting.
Self contained: KaTeX has no dependencies and can easily be bundled with your website resources.
Server side rendering: KaTeX produces the same output regardless of browser or environment, so you can pre-render expressions using Node.js and send them as plain HTML.
KaTeX supports all major browsers, including Chrome, Safari, Firefox, Opera, and IE 8 - IE 11. A list of supported commands can be on the wiki.

Javascript program emulating a pdp-11 running v6 unix.

A visual tool for wiring the Internet of Things.

Highcharts is a charting library written in pure JavaScript, offering an easy way of adding interactive charts to your web site or web application.
Free for non-commercial use. Found via
http://blog.tafkas.net/2012/10/03/gathering-and-charting-temperatures-using-rrdtool-and-highcharts/

An emulator of the M3 and M4 Enigma models written in JavaScript.

It translates a subset of Common Lisp to Javascript
+ bignum arithmetic
- no SQRT, SIN, ATAN, FORMAT, APROPOS
- #x and #.r upset the reader
See also the author's blog http://davazp.net/2013/01/04/lisp-to-javascript.html