Cross Platform Open Source C Code Library
Mongoose Web Server
Mongoose is an easy to use cross platform web server that can be used as an embedded web server library to provide web interface to applications or be standalone. It's executable is not dependent on any external library or configuration. If some additional config is required - for example, different listening port or IP-based access control, then a mongoose.conf file with respective options can be created in the same directory where executable lives.
jx9 Scripting language
Jx9 is an embeddable scripting engine that implements a Turing complete programming language based on JSON for use in applications such as games, database systems, text editors, network applications and so forth.
UnQLite is a software library implements a self-contained, serverless, zero-configuration, transactional NoSQL database engine. UnQLite is a document store database similar to MongoDB, Redis, CouchDB etc, as well a standard Key/Value store similar to BerkeleyDB, LevelDB, etc. UnQLite is an embedded NoSQL datastore engine. Unlike most other NoSQL databases, UnQLite does not use a separate server process and reads and writes directly to ordinary disk files. A complete database with multiple collections, is contained in a single disk file.
Currently at pre-alpha but testable and an interesting project, Tox is a P2P IM and VOIP cros platform client using strong encryption to guarantee privacy of communication.