S2 is a library for spherical geometry written primarily by Eric Veach:

• Designed to have good performance on large geographic datasets.
• Organized as a toolkit with various layers, that gives clients as much control as possible.
• Works exclusively with spherical projections.
• API available in C++, Go, Java and Python.
• Supports Linux and MacOSX.

a GUI-based application for viewing and processing spatial data. It includes many functions common to other popular GIS products for the analysis and manipulation of geospatial data.

free Java-based GIS tools