This extension gives Inkscape the ability to read and write Linerider (.sol) files
Virtually anything in inkscape can now be placed in your Linerider tracks, not to mention easy straight lines, beziers (curved lines), zooming, erasing, modifying nodes, text, shapes etc.
But enough talk - here come screenshots:
The Inkscape editing Window
Text and Shapes
I wrote a small tutorial at the Linerider.org forums (which were most probably how you found out about this):