Threads are different from goroutines. A Go program can create 100'000 goroutines, if it makes sense for the algorithm. Try doing this with threads... Super-cheap threads open many possibilities, it's a significant change in how you think and design programs.

Among your examples, those that are comparable to goroutines are all for functional languages. There's nothing wrong with functional languages, but it's far from "all mainstream languages".

Yes there are, they are known as user space threads or fibers.

User space threads don't run in parallel, i.e. they don't take advantage of multi-core CPUs and can be blocking.

Fibers are for cooperative multitasking so no parallelism either.

Goroutines are multiplexed as needed onto system threads. http://golang.org/doc/GoCourseDay3.pdf

So they are a bit different, in the spirit of Go: they make for a simple and general solution to both parallelism and concurrency. They combine naturally with channels to give the functionality of OS threads, user threads and fibers.

As an aside: watching Pike's talk on lexing and parsing in Go really hits this point home. It shows how language support for cheap threads (goroutines) and channels really change the way you come up with an algorithm.

http://www.youtube.com/watch?v=HxaD_trXwRE