Collecting examples for as many languages and related programming environments for “Hello world!” program: http://www2.latech.edu/~acm/HelloWorld.html.

Rosettacode’s idea is to present solutions to the same task in as many different languages as possible, to demonstrate how languages are similar and different: https://rosettacode.org/wiki/Hello_world/Text.

Updated in 2021: A little rust sample as I’m writing a lot in Rust nowadays:

fn main() {
    println!("Hello world!");
}

You can even write Hello World with zero line of code, and in rust it is a perfect 42 bytes!

/**/fn main(){print!("Hello, World!")}/**/