REBOL
REBOL is a lightweight, minimalist programming language designed for easy communication between distributed systems. It is mainly used for creating networked applications and scripting tasks across different platforms and devices.
Hello, world code example:
print "Hello world!"
Popularity: Less than 1% of developers are using or have used this language.*
*According to StackOverflow's 2023 survey.
Repositories on GitHub: 31,679