What good CAD programs are available?

See for example

• 6 of the Best Free Linux CAD Software
• The LUnIx Linux CAD Links: Extensive list of more than 50 alternatives with their licence type.

Not exactly the same as Solidworks or Autocad, but it really depends on what you are going to do. Reviews says that many free software do have good quality, but unfortunately that's really subjective.

You could try FreeCAD or BRL-CAD or some of the other floss alternatives.

VariCAD

It is a good and professional CAD Solution. It is available for Ubuntu. Since it is not OpenSource you can download a free trial version, it will works just like the full version for a period of 30 days. Require registration before.