Lots of Rubies around

I recently came across this blog post, where someone compared various implementations of Ruby, specifically to check the speed of each. When I read this post, I wasn't surprised at the results. I was totally surprised at how many different Ruby implementations there are. I hadn't realized how many there were.

Now, my question is, why are there so many different implementations that run Ruby code? I haven't read about the others, such as Rubinius or Cardinal, so I still don't know. I would imagine that there's different needs for each (such as Gardens Point Ruby .NET, as the name suggests). But unless there's a reason to have all these different ports, I wonder why there are so many.

Why don't these developers focus on the original Ruby language and strive to make it better, instead of forking off to a different road and possibly confusing new users? Like I said, I haven't read about these other implementations, so there may be something behind this. I'll take the afternoon to read about the other implementations, and try to find out why there's so much interest in making different Ruby implementations instead of focusing on the original.