The Courier Unicode Library implements several algorithms related to the Unicode Standard: look up of uppercase, lowercase, and titlecase equivalents of a Unicode character, grapheme and work breaking rules, line breaking rules, and several other related functions. The library also implements C++ bindings for these algorithms.
WhiteDB is a fast, lightweight graph/N-tuples shared memory database library with a focus on speed, portability, and ease of use. There is no server process. Data is read and written directly from/to shared memory. No sockets are used between WhiteDB and the application program. It supports indexes (T-tree), persistence through logging and memory dumps, concurrency through locking, limited queries (conjunctive only), JSON, CSV and RDF support, Python bindings, command line utility tools, and JSON REST tools.
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).