occam

Occam is a concurrent programming language that is based on the communicating sequential processes (CSP) model. It is primarily used for developing real-time and parallel applications.

Hello, world code example:

#USE "course.lib"
PROC main (CHAN BYTE screen!)
  out.string("Hello world!*c*n", 0, screen)
:

Popularity: Less than 1% of developers are using or have used this language.*
*According to StackOverflow's 2023 survey.

• Wikipedia page