I've been playing with http://nanocad.com which is an AutoCad look-a-like. It's strongest feature so far is true native DWG for trading files with others.
Also not a Vectorworks Spotlight replacement, just a free CAD, not even a true CADD.
For the purposes of plotting, programs such as SketchUp and Draftsight are not true alternatives to Vectorworks. The simplest and least expensive program is LXFree, which is available as an App for Mac, or as a Java program for Windows. Like Vectorworks Spotlight, it includes tools for labeling instruments with things such as channel number, gel color, etc. It also has rudimentary paperwork generating capabilities, although you can also get things into LightWright if you copy and paste some data into Excel first. A paid for version includes basic rendering and allows you to create custom instruments.