Draftsight is a good alternative for Autocad. Works on Windows, Linux an Mac.
I found it difficult to switch from Windows to Linux due to the lack of certain programs, like Autocad or Photoshop. It took me time to find an alternative and so I was always frustrated and returning to Windows. You can find some Cad programs and Linux, but the most of them feel difficult and not intuitive. Beeing Draftsight almost a “clone” of Autocad, the switch feels quite natural (the free version has some bugs, though). Once I started using it I could finally forget about Windows dual boot (Photoshop was the other problem, but there are also alternatives, and not just Gimp).
Draftsight is a product from Dessault Systemes (Catia, SolidWorks…) and has a free and a professional version. It’s fully compatible with Autocad (saves as .dwg and opens dwg files, although not the latest, at least in the free version). It’s just 2D, but it will fit your needs if you are been working with autocad. The professional version accepts autolisp and other advanced tools.