GeoTools is an open-source Java library for geospatial data manipulation, implementing OGC standards and providing a modular architecture for data access, styling, rendering, and coordinate reference systems. It supports a wide range of vector and raster formats through JDBC plugins (PostGIS, Oracle, SQL Server, etc.), shapefile, GeoPackage, GeoTIFF, NetCDF, and more. The library is used as the foundation for GeoServer and other GIS applications, offering a rich set of filter functions, process framework, and XML binding infrastructure for OGC web services (WMS, WFS, WCS, WPS). The codebase is well-structured with extensive test coverage, though some modules are marked as unsupported and may have lower maintenance priority.