Go to http://www.cadhistory.net for a link to a free e-book on the history of CAD (mostly oriented towards Mechanical CAD, but there are chapters on different companies). You are encouraged by the author to donate for the research on cancer.
The acquisition of Caligari (creators of Truespace) by Microsoft has lead to the release of Truespace 7.6 for free. Microsoft hopes it will help people to create content for their Virtual Earth system, not unlike the use of the free version of SketchUp to create models for Google Earth... This is a full version, including modeling, animation, rendering and customization, but for Windows only. And you have to get used to the icon-based interface (hundreds of icons for most functions. The interactive widgets in the viewport and the realtime rendering features in the modeling view are compelling features.