GeoMesa is a suite of tools for working with big geo-spatial data in a distributed fashion.

Java port of the Proj.4 library for coordinate reprojection

LocationTech Spatial4j: A Geospatial Library for Java

GeoGig project

LocationTech SFCurve is a Scala library for the creation, transformation, and querying of space-filling curves

GeoTrellis is a geographic data processing engine for high performance applications.