mMass is a free mass spectrum viewer/analyzer in which the following proteomics-related tasks can be performed: . - Open raw text, mzXML and mzData mass spectra; - Define peak lists; - Powerful mass spectrum viewer (zoom, cursor...); - Data recalibration; - Protein-only simulations; - Online Mascot searches. . This software is written with Python, and the author claims that writing new modules should be easy.