Like others have already mentioned it does (at first glance) seem have a passing resemblance to Io (http://iolanguage.com).

Here is the Greeter example in Io:

    Greeter := Object clone

    Greeter new := method (n,
        Greeter clone do (name ::= nil) setName(n)
    )

    Greeter sayHi := method (
        (name .. ": Hi!") println
    )

    Greeter new("Alex") sayHi

Very close. However even though I've tried to make it look identical you can see the differences poking through. And reading through the Atomo docs there are (naturally) other divergences.

I would say that Atomo is probably more closer to Ioke (http://Ioke.org) than Io. The philosophy behind Io is to keep it small & simple. Whereas Ioke is Io + extra syntax, literals, etc baked in.

Worth keeping an eye on Atomo... as is Io & Ioke. For reference here are the other examples in Io:

    File with("out-file") open do (
        write("hello, world!\n")
    )

    fib := method (n,
        if (n == 0, return 1)
        if (n == 1, return 1)
        fib(n - 2) + fib(n - 1)
    )

    list(1, 2, 3) sum
    Range 0 to(5) map(* 2)