libdwarf reads and/or writes DWARF debugging information in Elf object files. dwarfdump uses libdwarf to read object files and print the DWARF content in a readable fashion. libdwarf implements the DWARF2 (and later) standard by providing function interfaces that abstract away many DWARF implementation details (the writer code only emits DWARF2 so far). The source also includes implementations of a few tree search (tsearch) algorithms (balanced, red-black, and binary).
cparser is a recursive descent C99 parser written in C99. It contains a lexer, parser, constructs an AST, and does semantic analysis. It is currently used as a frontend to the libFirm intermediate representation, but can be used independently. It supports lots of GNU extensions: enough to parse Linux/BSD system headers and compile typical C projects with it. It is able to bootstrap itself, and compiles and runs the spec CINT2000 without problems.
The libjit library implements just-in-time compilation functionality. Unlike other JITs, this one is designed to be independent of any particular virtual machine bytecode format or language. Currently, libjit is used as the JIT backend for the DotGNU Portable.NET project (in addition to its default CVM backend). However, the hope is that other Free Software projects can use this library rather than spending large amounts of time writing their own JIT from scratch.
linux-libc-headers is a set of Linux kernel headers for building libc. Since Linux 2.6, the kernel authors have frowned upon userspace programs including the kernel headers directly. Instead, the recommendation was to use sanitized kernel headers for userspace programs. The Linux Libc Headers project provides such a set of sanitized headers. It was initiated as a PLD Linux specific project.
mdocml is a suite of tools for compiling "-mdoc", the roff macro package of choice for BSD manual pages, and "-man", the predominant historical package for UNIX manuals. The mission of mdocml is to deprecate groff, the GNU roff implementation, for displaying -mdoc pages whilst providing token support for -man.