List of OSS or free STEP programs

Software used in SCL development
Express Engine - used by SCL to validate models with schemas. Old website is here

Other Free Software for STEP
IDA-STEP Viewer - free downloadable STEP file viewer

Jen-X p28 schema generator and p21-p28 mediators - for shipbuilding STEP AP's

STEP Tools - free on-line EXPRESS schema checker

STEP-toybox

Express for Free, also here

JSDAI

Reeper

OntoSTEP Protégé plugin

SEBNF2Pars - Creates Part 21 parsers from an EBNF representation

lgtstep - a Logtalk STEP implementation

Scripting Applications for STEP Part 21 files - uses Prolog

http://github.com/mvaerle/python-ifc

http://www.ifcgears.com/extender.php

Commercial
ST-Developer