Simple interpreter, runs on Java VM, with 3 visual aids/tools to support learning functional programming via Scheme; has viewers (environment, function call, cons-cell), i.e., global environment, recursive trees, linked list. Description, thesis, scre...

Jonathan A. Rees's unofficial page: history, links, status.

Fairly detailed, by Olin Shivers.

Old site, last update 1997. Embeddable, reusable extension language subsystem for applications written in C/C++, also a useful standalone Scheme implementation with interfaces to POSIX, Unix, X11.

A portable Scheme implementation written by Aubrey Jaffer.

Two systems for Windows with built in "industrial-strength" solid modeler based on the ACIS solid modeler Geometric Modeling Kernel.

Interpreter for Macintosh or Windows. Has "friendly and convenient interactive programming environment" with language sensitive editor, full documentation. [commercial, free 14 day download]

A fast, small Scheme interpreter which is mostly compliant with the R5RS standard.

Very small, portable implementation, has some database, Unix programming, CGI scripting extensions. Runs on DOS, Linux, Unix, Windows. Free source downloads.

A superset of the Scheme dialect of Lisp with extensions to support object-oriented programming.