How to draw straight lines in free snaping?

I would like to know how could i "snap" in axis while in free snapping mode.

I dont want to use the orthogonal restriction. I'm more interested in the feature similar to AutoCAD ou Floorplanner: while i'm moving the line freely, it snaps in axis for draw a straight line.

With all snaps off, press and hold the [Shift] key while drawing a line.  It constrains the line to 15 degree intervals.