Home page: www.plt-scheme.org
PLT Scheme is an umbrella name for a family of implementations of the Scheme language: DrScheme, MzScheme, MrEd.
DrScheme is a graphical programming enviroment, which runs on all major platforms. DrScheme provides source highlighting for syntax and run-time errors, support for multiple language levels, an algebraic stepper, objects, modules, a GUI library, TCP/IP, and much more. It includes an extensive, hyper-linked help system called Help Desk, available from the Help menu. The Tour of DrScheme describes many of these features in greater detail. The Schematics Scheme Cookbook and #scheme-on-freenode are valuable learning resources. Another resource on the design of PLT Scheme is the DrScheme paper.
For scripts and non-gui programs, PLT Scheme provides MzScheme, which runs in text mode. It can be used for scripts, or for developement together with Emacs.
PLT Scheme provides a compiler mzc, which produces native code via C.