Leveller is a powerful 3D terrain editor for windows from Daylon Graphics. With Leveller the user can "paint" terrain, use vectors to create contours (which can then create heightfields) and use a variety of filters and tools to create distinctive and realistic terrain features (see the website for a more complete list of features). Users can also import and export heightfields in a variety of formats, and the latest update includes methods to easily import from and export to terrains with OpenSimulator (Opensim for short). This tutorial gives a run though on how to do that and why.
Read the full article here: http://asstnotesideas.blogspot.be/2017/02/leveller-for-opensimulator-part-1.html