Although the alternatives on Linux may not be so powerful as AutoCAD, the two programs I will talk about here are free and have enough features to create 2D ample projects.
DraftSight is developed by Dassault Systèmes, a French company specialized in CAD design. On the website you can find both the free and a paid, Pro version.
DraftSight is written in Qt and has a similar interface to AutoCAD for Windows: