PBL (The Program Base Library) is a C library of array/linked list, hash/tree set, and key file functions that can be used in a C or C++ project. It is highly portable and compiles warning-free on Linux gcc, Windows Cygwin gcc, Mac OS X, and Windows Microsoft Visual C++ 2008 Express Edition.
liblfds is a portable, lock-free data structure library. Out-of-the-box ports are provided for Linux (user-mode) and Windows (user-mode and kernel-mode) on ARM, x86, and x64, under a variety of toolchains. Currently, the library contains a freelist, queue, ringbuffer, singly-linked list (logical delete only), and a stack. The homepage contains a blog, bugzilla, forum, and mediawiki. The mediawiki contains comprehensive documentation for development, building, testing, and porting. There is no license. You are free to use this code in any way.
cola is a C implementation of the COLA structure described in the paper "Cache Oblivious Streaming B-Trees" by Bender, Farach-Colton, et al. This algorithm is a drop-in replacement for B-Tree databases/indexes which performs faster on spinning disks than B-Trees do on SSD. It's asymptotically optimal in terms of data transfers to and from disk. For example, random key inserts are turned into linear sequential writes while maintaining the property which queries always require, at most, precisely log N blocks read sequentially (but not contiguously) from disk (or half that, on average).