Recs.
Updated
Scheme is a functional programming language and one of the three major dialects of the programming language Lisp. (The other two being Common Lisp and Clojure.)
Specs
Pros
Cons
Con Very different semantics from mainstream programming languages
LISP-like languages are very different from mainstream languages (such as C/C++/Java/JavaScript/Python/you-name-it) - both in semantics and syntax. This, in turn, severely limits uses of whatever-learned-with-Scheme, for real-world use.
Con Fragmented ecosystem
Scheme is an IEEE standard, not an implementation. Unfortunately, the standard is too minimal and practical implementations have diverged--they had to expand on the standard to get anything done, but did so in incompatible ways.
The later de facto standard R6RS tried to correct this, but lost Scheme's minimalist elegance in the process. The newer R7RS standard takes the best of both worlds with an elegant minimalist core and a practical standard library.