Cool is a Classroom Object-Oriented Language — it contains a number of programming language features common in other object oriented languages (such as Java). It's small enough to be manageable for semester projects but large enough to help you to learn all of the concepts and to write non-trivial programs.
The Cool programming language is formally specified and defined in The Cool Reference Manual, a document that you will grow to love (or hate) over the course of this semester. Multiple versions are available:
Different versions of the reference interpreter are available for different platforms. Information on running the interpreter is available in the reference manual.
There is Cool syntax highlighting support for Vim.
If you like XEmacs, the Berkeley Harmonia project has a Cool mode. It offers quite a bit more than syntax highlighting, but not all of the semantic features are guaranteed to be compatible with our dialect of Cool.
The Sublime text editor supports Cool syntax highlighting.
The Atom text editor has a student-written Cool language syntax highlighter.