Arpeggio is done or influenced by the following free tehnologies.

Python Programming Language (http://www.python.org)
    - Arpeggio is implemented 100% in Python programming language.
    
PyPEG - a PEG Parser-Interpreter in Python (http://www.fdik.org/pyPEG/)
    - PyPEG is a parser interpreter based on PEG grammars like Arpeggio but
        with different design and implementation approach and different goals in mind.
        The idea of Arpeggio parser definition using Python language constructs is
        taken from the PyPEG project. Arpeggio also supports parser definition using PEG
        textual notation.
    
pyparsing (http://pyparsing.wikispaces.com/)
    - pyparsing is IMO currently the most advanced parser written 100% in python.
        Currently there is no much similarity between pyparsing and Arpeggio but
        there are some nice features and ideas from pyparsing that I think would be nice to 
        have implemented in Arpeggio.
    

Although not directly related to Arpeggio I wish also to thank to the 
following free software projects that makes the development of Arpeggio (and some other 
projects I am working on) easier and more fun:

- Arch Linux (http://www.archlinux.org/) - Linux distro that I'm using on my dev machine.
- Editra (http://www.editra.org/) - Nice programmer's editor written in Python and wxWidgets.
- Mercurial (www.selenic.com/mercurial/) - Distributed version control system written in Python.

... and many more