Tools and SDK
MULTOS SmartDeck - Develop smart card applications, for free!
MULTOS SmartDeck is a complete high-level language application development system for MULTOS that combines all the features that you need to develop compact, efficient programs using 'C', assembler and the Eclipse IDE. You can register for and download a copy here. Please report any problems using the Developer Support contact form or if you are a forum member please ask a question there.
There are some introductory slides to using SmartDeck with Eclipse here.
MUtil - A simple to use, multi function tool for managing content on MULTOS and step/one smart cards. Documentation for this tool can be found in the Technical Library.
ROM keys for live masks are published on the StepNexus website.