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.