This is ILLGOL, a communicable disease disguised as a programming language, running under FreeDOS running on a web page via the HTML5-based IBM PC compatible emulator, v86.
Instructions:
The system that v86 runs is delivered on a 720K floppy image,
which contains a minimal bootable FreeDOS install, the ILLGOL distribution,
plus various tools such as the TED3 text editor.
License and distribution information is included on the disk image.
You can use these tools to build and run ILLGOL programs.
See the welcome message, shown after FreeDOS
boots, for more details.
If v86 doesn't work in your browser, you can
download the disk image
and use it in an emulator such as QEMU or DOSBox
or, wonder of wonders, a real IBM PC compatible — if you can write it onto
a floppy disk somehow...