The GNU Compiler Collection contains frontends for C, C++, Objective-C, Fortran, Java, and Ada as well as libraries for these languages. It is a full-featured ANSI C compiler with support for K&R C as well. GCC provides many levels of source code error checking traditionally provided by other tools (such as lint), produces debugging information, and can perform many different optimizations to the resulting object code.
The GNU Debugger (GDB) is a source-level debugger for C, C++, Java, Modula-2, and several other languages. It runs on GNU/Linux, the BSD's, and almost every major proprietary OS. GDB can debug programs running on the same machine as itself, or it can communicate over a network or serial line with a debugging stub on another machine; thus, it can be used for embedded and kernel debugging.
TOra is a Toolkit for Oracle that helps the DBA or developer of a database application. It features an SQL worksheet with PL/SQL block parsing, a PL/SQL debugger and editor with syntax highlighting, a Schema browser, Unicode support, printing, and a full suite of DBA management tools.
ltrace is a debugging program which runs a specified command until it exits. While the command is executing, ltrace intercepts and records the dynamic library calls which are called by the executed process and the signals received by that process. It can also intercept and print the system calls executed by the program. The program to be traced need not be recompiled for this, so you can use it on binaries for which you don't have the source handy. You should install ltrace if you need a sysadmin tool for tracking the execution of processes.
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.