We recently posted about a free AutoCAD alternative called BRL-CAD, which is very advanced and build by the US military in collaboration with NASA. But the application is not that easy to use by normal people, not very much into CAD applications (or the army :-) ).
AutoCAD is one of the most expensive applications, but also indispensable for many types of jobs. Being so expensive, it's a good reason to look for free alternatives. QCad is one of the alternatives but sometimes it's just not enough.