Because the company no longer exists and Microsoft has abandoned the software (the 7.6 download links are now dead on Microsoft's official site), the software is considered . Downloading it from archive sites is generally accepted by the community as long as you are not using it for commercial resale.
Caligari Corporation was acquired by Microsoft in 2008. In 2009, Microsoft released TrueSpace 7.6 (the final version) as a free download on their Microsoft Download Center. However, Microsoft did not officially re-release versions 4.3 or earlier. Download truespace 4.3
When you launch TrueSpace 4.3, it will likely complain about missing DirectX drivers. Do not panic. Because the company no longer exists and Microsoft