PLT-Scheme is a set of tools for writing and running the PLT scheme
programming language.  It includes a graphical IDE (drscheme) that
features highlighting of the source of 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 plt-help command line tool, or through a
web browser.

mred is the interpreter/JIT compiler that includes the GUI toolkit.
drscheme is the GUI ide, and is a mred application.
mzscheme is a text-only variant that does not include the GUI toolkit.
swindle is a language variant that includes a CLOS-style object system.
mzc is a compilation manager that can produce stand-alone executable programs.
plt-r5rs and plt-r6rs are front ends for running standards-conforming
programms.
plt-web-server is a web server.
scribble, slatex and tex2page are text formatters.
slideshow is a presentation formatter.
sirmail is a mail user agent.

WWW: http://www.plt-scheme.org/