Ell is a library to write EBNF grammars as C++ code for quick development of LL(n) parsers or similar applications. It is not a tool to generate parsers (like ANTLR): the grammar you write is directly embedded into your C++ code. The core library is very light (less than 2000 lines of headers) and written in generation templates to achieve the fastest execution. The service provided by Ell is very similar to what Boost Spirit provides, but with a simpler object model, and without the need of the Boost library (it only depends on STL).
YAJL (Yet Another JSON Library) is a small event-driven (SAX-style) JSON parser written in ANSI C, and a small validating JSON generator. It's highly portable, data representation independent, fast, generates verbose error messages including context of where the error occurs in the input text, can parse JSON data incrementally off a stream, and is tiny.
The Parsing Expression Grammar Template Library (PEGTL) is a C++0x library for creating parsers according to a Parsing Expression Grammar (PEG). Grammars are embedded as regular C++ code, created with template programming (not template meta programming). These hierarchies naturally correspond to the inductive definition of PEGs. The library extends on the subject of PEGs with new expression types, actions that can be attached to grammar rules, and mechanisms to ensure helpful diagnostics in case of parsing errors. PEGs are superficially similar to Context-Free Grammars (CFGs).