It just recently got official support for Windows and Linux, and it had low-key Linux support for a while before that. I've heard of people writing web servers in it. Like Go, it compiles directly to native machine code.

Isn't it still slower than GO because of referencing counting?

Depends what you mean by slow. Go is garbage-collected, Swift is reference-counted. Each has advantages and disadvantages. But also, that doesn't apply to stack-allocated values. It's not as simple as one being faster than the other.