The Kawa Scheme System is a full Scheme implementation, completely written in Java. Scheme functions and files are automatically compiled into Java byte-codes. Kawa does some optimizations, and the compiled code runs at a reasonable speed. It provides the usual read-eval-print loop, as well as batch modes. The Kawa compilation framework is also useful for implementing other languages on top of JVM. There is active development of XQuery (the XML query language), and less active development of Emacs Lisp, Common Lisp, and EcmaScript.
Scsh is a systems-programming environment for POSIX systems and Win32, embedded in the Scheme programming language. It includes a high-level process notation for writing shell-script like programs, with pipelines and redirections. Scsh additionally provides low-level access to POSIX primitives, plus important non-POSIX extensions such as sockets. Scsh is implemented on top of Scheme48, a portable bytecode implementation of Scheme. A number of user-contributed extensions are available, including an extensible HTTP and FTP server, a socket-level PostgreSQL interface, a programmable text formatting language, and a Postscript generation language.
Kahua is a continuation passing style (CPS) application framework and server. It is written using the Gauche implementation of Scheme. It has the advantage that you can use "continuations" easily, so you can solve the typical Web application's problem of process disconnection. It allows you to program declaratively by using S-expressions as a fundamental data type, you can use Kahua's Object Database to persist data, and you can modify the function being run, supporting incremental development.