avrmon-stk200 is a port of Denis Chertykov's Linux debug monitor system for Atmel AVR microcontrollers. It is compatible with the connection scheme used in Atmels "STK200 Starter Kit", as opposed to the original version that used the "DAPA" (Alex's Direct Avr Parallel Access) scheme. In short, the monitor system allows you to do in-systems source-level debugging on AVR microcontrollers with gdb (avr-gdb).
Libcwd is a full-featured and well-documented library that assists C++ developers with debugging their applications. It includes support for ostream-based debug output, custom debug channels and devices, memory allocation debugging, run-time sourcefile:linenumber information, and demangled type names of variables. It is thread-safe.
CMUCL is a free, high performance implementation of the Common Lisp programming language which runs on most major Unix platforms. It mainly conforms to the ANSI Common Lisp standard. CMUCL provides a sophisticated native code compiler; a powerful foreign function interface; an implementation of CLOS; the Common Lisp Object System; which includes multimethods and a metaobject protocol; a source-level debugger and code profiler; and an Emacs-like editor implemented in Common Lisp. CMUCL is maintained by a team of volunteers collaborating over the Internet, and is mostly in the public domain.
Code Medic provides access to the power of gdb with an intuitive front end. It currently supports opening multiple source windows at once, setting/clearing breakpoints while the program is running, watching variables change in the variable tree as you step through code (even with nested structs), text searching through source, and integration with Code Crusader to provide a rapid, efficient develop-debug cycle.
Java Development Environment for Emacs (JDEE) is an Emacs-based integrated development environment (IDE) for developing Java applications and applets. Features include multiple code browsers, a JPDA-based debugger, method and field completion, template-based and procedure-based code generation, Java source code interpreter, context-sensitive help, and more.