GNU tool chain
Given a large project on GNU/linux, it's often necessary to first cross reference the code, getting a higher level overview of the data structures, generate man pages of essential APIs and data types.
The following tools are my favorite
1. umbrello, for creating high level UML diagrams of essential data structures and APIs
2. cscope, ctags to generate cross reference, sometimes I also use lxr for c/c++ projects
3. creating man pages, this generally involves a few shell scripts and perl scripts to convert html document to man page.
4. use small test programs to understand the existing framework's APIs and design structure.
During the process, I found it's essential to have a basic knowledge of the following GNU toolchain to make a developer's life easier:
1. bash scripting. Writing bash script is like writing assembly, succinct, efficient, and to the point. One additional trick is the bash built in 'help' command to look up information on bash builtin commands, e.g. 'help for'
2. vim or emacs. After 13 years of vim, there are still new things to be learnt, this is a keybind macro I devised recently to lookup C++ stl API/data structures directly from SGI website inside vim (look at the html source code directly to see how this macro is done, there is no direct way to expose it through blogspot):
: !links -dump http://www.sgi.com/tech/stl/ =expand(' ') .html\|vim -R -
Enter visual mode (v), highly your keyword, and push Ctrl+k, this will take you to another vim session with the page downloaded and formatted. Isn't it neat?
3. makefile. It's naive to think of makefile/make as only a compile/link tool. It's more than that. Ever notice its similarity with the EBNF form in terms of structure? Yes it's actually an automaton, a complete turing machine. It can be literally used to perform any task C/C++/Perl etc can do. Its EBNF structure provides a powerful and intuitive hierarchical approach to resolve difficult problems.
4. The old and good man page. Use 'shift+k' inside vim on a keyword (non visual mode) to get its man page, this is default installed in vim. Typically MANPATH is the search path for man pages. I have not found a good way to break up long lines in man pages. COLUMNWIDTH etc does not seem to affect man page generation from a text file with troff.
4. Bash Cookbook solutions and examples for bash users
5. Hacking vim a cookbook to get the most out of the latest vim editor
6. http://www.gnu.org/software/make/manual/make.html (unfortunately there is not a single book available to systematically introduce gnu make to general public. The manual remains the sole source of comprehensive explanation of gnu make)