Elastizell Corp.
We manufacture cellular lightweight concrete and lightweight fills. Elastizell is America's Industrial leader in cellular concrete applications for: Insulating Concrete Roof Decks, Engineered Fill Geotechnical Applications, and Non-Structural Floor Fills
http://www.elastizell.com/

Advanced Lightweight Engineering
Specializes in design, development, and production of lightweight structures. Based in the Netherlands.
http://www.lightweight.nl/

Tensys
An engineering analysis consultancy providing specialist services for the design and construction of lightweight stressed membrane structures worldwide.
http://www.tensys.com

Cellxion
CellXion designs and manufactures a full line of concrete, structural steel, and ultra-light aluminum shelters. In addition to shelters, CellXion provides specialty products such as cell-on-wheels, cell-on-chassis, and tower trailers. Services include equipment integration and complete turnkey construction.
http://www.cellxion.com/

LGI (Lightweight GUI Library)
A Lightweight, cross-platform GUI library and application framework. Currently 3 ports exist, Win32, Linux and BeOS. [Open source]
http://www.memecode.com/lgi.php

California Lightweight Pumice Inc.
Pumice - Suppliers of pumice, lightweight concrete, lightweight backfill, lightweight aggregate and pre-cast block products
http://www.clppumice.com/

Simple Building Systems
Pre-cast and cast-on-site lightweight concrete and steel panels used for the construction of walls, floors and roofs on tilt-up and metal buildings
http://www.simplebuilding.com

PlaneWave Instruments
The goal of PlaneWave Instruments is to create high quality imaging telescopes at an affordable price. Our primary focus is on product performance, customer service, and quality workmanship.
http://www.planewaveinstruments.com/

Scarab: Lightweight Distributed Objects
A lightweight scheme for representing distributed objects providing both a compact binary protocol as well as XML-based serialization. Used as part of the Casbah project.
http://casbah.org/Scarab/ldo.html

Lightweight Foam Concrete Made Easy
Provides equipment, chemicals and training for making lightweight foam concrete. Based in Asia
http://www.portafoam.com/