From the chat...
From the web page:
Therion is a complete package which processes survey data and generates maps or 3D models of caves. It runs on wide variety of platforms: Linux, Windows, Mac OS X. It is completely free, released under the terms of GNU GPL, with source code available. It doesn't require any other commercial software to run.
Basic drawing instructions [L2 ]
...and an example of a map drawn with Therion: