STklos is a free Scheme System conforming to R5RS. The implementation is based on an ad-hoc Virtual Machine. It can also be compiled as a library, so that one can easily embed it in an application. Its features include an efficient and powerful object system based on CLOS, a simple-to-use module system, implementation of the full tower of numbers defined in R5RS, and easy connection to the GTK+ toolkit. STklos is the successor of STk, a Scheme interpreter tightly connected to the Tk toolkit.
Sizzle is a Scheme interpreter for embedding into C applications and for standalone scripting. It implements a nearly complete subset of R5RS Scheme, adding a lot of primitives for U*ix scripting, regular expression searching, a simple module system, dynamic library linking, powerful string processing procedures, and much more. It includes a user's guide and an embedding manual in texinfo format, some examples, the embedding library, and a standalone interpreter for interactive use and scripting.