Mechanical, HVAC and Plant Design

Alias ltd.
Offers the Isogen software for plant design, as well as related modules for isometric presentation, data conversion, and 3D modelling.
http://www.alias.ltd.uk/

Camatic, Ltd.
Software for plant and ship design and engineering, as well as for managing the maintenance during lifetime.
http://www.cadmatic.com/

Cea Technology
Makers of the Plant-4D plant design application for AutoCAD and Microstation, and related software modules.
http://www.cea-int.com/

Cymap Building Services Software
Design software for HVAC, lighting and electrical design. Covers CIBSE/DIN/ASHRAE design standards, available in English, German, Hungarian
http://www.cymap.com

ETank, Inc.
Software for calculating steel and aluminium storage tanks according to US standards, and management tools for plant equipment maintenance.
http://www.etank.com/