OpenJUMP is an open source GIS software. It is based on JUMP GIS by Vivid Solutions. Features:
OpenJUMP is a Vector GIS that can read rasters as well.
OpenJUMP works, even with medium size datasets, and with professional touch.
OpenJUMP provides a GIS API with a flexible plugin structure, so that new features are relatively easy to develop around the sound mapping platform.
OpenJUMP utilizes standards like GML, WMS and WFS.
* OpenJUMP supports a couple of languages (English, Finnish, French, German, Portuguese and Spanish).
JUMP 1.1 User Guide
JUMP Developer Guide