One of the difficulties in getting started with the Scheme programming language is picking an implementation. There are a bunch. Many of them are very good. Each has strengths and weaknesses. But those strengths and weaknesses don’t always readily line up with uses. So, recommending an implementation can be tricky.
Here is a pretty good guide to picking an implementation: “an opinionated guide to scheme implementations”
I know a lot less about Scheme than (wingo). I just play with it and use it instead of Bash/Perl/Python/Ruby whenever I can at work. Still, I was a Scheme newbie once, so here’s my suggestion:
If you’re using Linux or BSD, check to see if Guile is installed. (If you’ve got Mac ports or fink installed on your Mac, you might fall into this category as well.) There are things I love about Guile, and there are things I hate about it. But it is hard to argue with it already being installed on your machine. Grab a copy of SICP or The Little Schemer or whatever and go...
If you’re on Linux or BSD and you don’t have Guile installed, check your package manager for it.
If you don’t have Guile or if you’re ready for something more than Guile, get Racket. While the people working on Scheme standards are trying to figure out how to please academics and pragmatists, Racket has built a Scheme that is good for learning/teaching the language and has much of the “batteries included” that some other languages claim you should expect.
If you want Racket but without the GUI bits, you’ll have to dig a bit for Racket Textual.
Once you’ve had a taste of Scheme with Guile and/or Racket, then you can start to delve into what makes all those other implementations unique.