The MongoDB C Driver is a 10gen-supported driver for MongoDB. It’s written in pure C. The goal is to be super strict for ultimate portability, no dependencies, and generic embeddability.
The driver is still considered alpha but is undergoing active development. Support for replica sets was just added in v0.3.1. The API was completely revamped in v0.4. Another backward-breaking change (support for write_concern) was added in v0.6. Default write acknowledgement with mongo_client and BCON (BSON C Object Notation) were added in v0.7. Uniform init/destroy pairing, improved support for 64-bit architectures and Windows, enhanced GridFS are in v0.8.