The c prototyping tools library provides generic tools for application development in plain c covering basic data structure implementations, persistence, threading and tcp and http communication. lgpl
Why another XML library? Because it is fast, easy-to-use and -important- it is my personal work about the second layer of the Semantic Web. LGPL 2.0 license
The PCRE library is a set of functions that implement regular expression pattern matching using the same syntax and semantics as Perl 5. PCRE has its own native API, as well as a set of wrapper functions that correspond to the POSIX regular expression API.
Knit is the first component definition and linking toolset from the Alchemy project. Knit helps to make C code more understandable and reusable by third parties, helps eliminate much of the performance overhead of componentization, detects subtle errors in component composition that cannot be caught with normal component type systems, and provides a foundation for developing future analyses over C-based components, such as cross-component optimization.
Bow (or libbow) is a library of C code useful for writing statistical text analysis, language modeling and information retrieval programs. The current distribution includes the library, as well as front-ends for document classification (rainbow), document retrieval (arrow) and document clustering (crossbow).
A library of generic C modules; also, excellent list of links to similar libs
linkedlist, hashmap, pool, stack, and varray, a flexible memory allocator, CSV parser, path canonicalization routine, I18N text abstraction, configuration file module, portable semaphores, condition variables and more.
Datadec takes recursive data types modelled on those found in functional languages (Hope, Miranda, Haskell etc) and generates ANSI C code to implement them.
The MLib (pronounced "M-Lib") is a C software framework that significantly simplifies the development of highly reliable system-level libraries and programs (like daemons/services). It is small, efficient, robust and highly portable, and was designed primarily for embedded systems. (From the FreeType project)