From: http://www.bravaviewer.com/free-dwg-viewer

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From: http://www.ida-step.net/components/viewers/basic

Viewer: Basic is a FREE component of IDA-STEP v4 providing core viewing functionality for all kinds of STEP files (*.stp). This component alone makes IDA-STEP v4 a fully usable tool for viewing PDM, CAD and other data, available as STEP (internation standard ISO 10303) files. STEP file format is supported by the major PDM, mechanical CAD and other systems. 

From: http://viewer.kisters.de/en/downloads.html

    3D-Viewer, 3D-CAD-Viewer and 2D-Viewer provided by KISTERS for efficient visualization
    Demo Download - NOT Free

From: https://shop.oracle.com/pls/ostore/product?p1=AutoVue&p2=&p3=&p4=

    Oracle AutoVue - AutoVue Enterprise Visualization is a suite of Oracle solutions designed to view,
    digitally annotate and collaborate on a variety of engineering, CAD and business documents without 
    requiring investment in specialized CAD or authoring tools. Customers can choose from amongst five 
    AutoVue solutions, each designed to suit an organization’s current and evolving document visualization
    requirements.

From: http://kubotek3d.com/Products/Spectrum-Viewer.aspx

    Kubotek Spectrum is low cost, professional-grade CAD viewer software for reviewing 3D models and drawings.
    AutoCAD™, SolidWorks™, and Pro/E™, UG NX, CATIA 4, CATIA 5 (Optional), IGES, STEP and many others.