Rats!

Rats! is an "easily extensible parser generator for C-like languages" written by Robert Grimm. The main idea of Rats! is to exploit the extensibility of PEGs by providing support for parametrizable grammar modules which can use, instantiate, extend and modify each other. Grimm describes version 1.8.2 of Rats! in Better Extensibility through Modular Syntax. More documentation can be found in the Rats! intro. It is part of the the extensive Javadoc of the xtc project, which is the framework project of Rats!. Here comes what I consider the main design principles, features and properties of Rats!.

OMeta

OMeta is an object-oriented language for pattern matching based on Parsing Expression Grammars (PEG). It makes some valuable extensions to standard PEGs which I want to summarize here. My main source of information is the paper OMeta: an Object-Oriented Language for Pattern Matching by Alessandro Warth and Ian Piumatra.

Stratego/XT

Stratego/XT is the first meta programming system I had a closer look at. The project defines itself as "a language and tool set for program transformation". By program transformation they mean "programming tasks using some form of automatic program generation or transformation, such as code generation from a domain-specific language, aspect weaving, optimization, or specialization of a generic program to a particular context." So Stratego/XT follows a more generalized approach then what MDE needs.