A couple interesting pieces of software I noticed recently:

• SQLite, an embeddable SQL database engine. It implements a nearly-complete subset of SQL 92, in 25K lines of public-domain source. Also has a impressive set of language bindings.
• Structorian is a binary file viewer that accepts C-like struct definitions to instruct it how to interpret data. It is at an early stage of its life (it needs polishing to make it feel second-nature), but looks very promising.