DrScheme
    DrScheme is a graphical, interactive programming environment. In addition to editing and interactive execution facilities, DrScheme also provides various student-friendly features, integrated library support, and sophisticated analysis tools for advanced programmers.

MrEd
    MrEd has two facets. First, it is a portable, cross-platform graphical toolbox used to build DrScheme and other applications. Second, it provides advanced linguistic facilities to enable process-like features within a single language run-time. Unless you intimately understand your needs, we recommend that you use DrScheme. MrEd is distributed as part of DrScheme.

MzScheme
    MzScheme is the underlying text-only implementation: it provides all of MrEd's features except the graphics library and the eventspaces. Its language offers several extensions to standard Scheme. The MzScheme executable is relatively small and loads quickly, and is designed to be used as an engine for executing scripts. Unless you need the restricted interaction mode, we recommend that you use DrScheme. MzScheme is distributed by itself and as part of DrScheme.