otl is a text processor for generating markup from readable lightweight markup. Much of both the input and output formats can be customized. HTML output is bundled as an example. otl supports complex structures such as nested ordered and unordered lists, headers and footers, and tables.
Fract is a Web-based fractal zoomer for the Mandelbrot set. It has no advanced features, for the goal is to keep the code easy to read for someone interested in fractals. The package also includes an offline renderer that you can use to generate high resolution images of your favorite spots. You can also easily play with the color map.
ACL2 is a mathematical logic, programming language, and mechanical theorem prover based on the applicative subset of Common Lisp. It is an "industrial-strength" version of the NQTHM or Boyer/Moore theorem prover, and has been used for the formal verification of commercial microprocessors, the Java Virtual Machine, interesting algorithms, and so forth.
SLIME is an integrated development environment for Common LISP which does everything you would expect from an IDE: code evaluation, compilation, macro expansion, and auto-completion. It also finds definitions of functions, and marks LISP forms which the compiler finds to be erroneous. It provides easy access to implementation-specific online documentation as well as the ability to look up symbols in the ANSI Common Lisp HyperSpec. Further, it includes an interactive debugger and object inspector.