Chicken is a Scheme compiler that translates most of R5RS Scheme into relatively portable C. It supports fully general tail-call recursion, first-class continuations, and has a very flexible and efficient interface to C and C++. Chicken implements several extensions to the Scheme language: lightweight threads, pattern matching macros, dynamic loading of compiled code, and various object-oriented paradigms, such as TinyCLOS, and others. The library system includes hundreds of convenient modules for practical use.
mu is a collection of utilities for maildirs, in particular for indexing and searching them. mu fills a database with information about your emails, which can then be queried using an easy query language. It can work stand-alone or be integrated with a mail client. It also provides an emacs-based email client ("mu4e") and bindings for Guile/Scheme.
InteLib is a library of C++ classes that lets you do Lisp/Scheme programming within your C++ programs, even without any additional preprocessing, without all those calling conventions. You can write code that is accepted by a C++ compiler while thinking in a "Lisp/Scheme mode", and the code you write will look much like Lisp/Scheme code, although it will be pure C++.
Meep is a free finite-difference time-domain (FDTD) simulation software package to model electromagnetic systems. It supports distributed-memory parallel simulations, nonlinear, anisotropic, and dispersive media, PML absorbing boundaries, and 1D/2D/3D and cylindrical problems. It is completely scriptable from either C++ or a Scheme (GNU Guile) interface.
travtrack is a tool to help a Traveller(tm) referee keep track of essential data for a game. Already implemented are galaxies, sectors, subsectors, systems, stars, planets, belt and moons. Yet to be implemented are trade routes, ships, characters, and all the rest. These will take some time, but should not be too complex. It currently uses the GURPS Traveller:First In rules for system generation, but a subproject is under way to add Classic Traveller generation and output. travlib is a collection of C routines that should make writing a Traveller application easier. A guile interface to the data representation functions is provided.
Kipt (Kizome's ISA Piercing Tool) is an HTTP proxy server and proxying name server with the ability to forward requests to other HTTP proxies or to get the documents directly from hosts. It can go through MS ISA Server or MS Proxy doing NTLM authentication. If you're stuck behind a restrictive firewall or proxy with at least one port open for outgoing connections and you have access to a machine outside, you can have nearly full Internet access by using this proxy and the socksify program from dante.