GeoServer is an open-source server for sharing geospatial data. It publishes data from many spatial sources, such as Shapefiles, PostGIS, Oracle Spatial, SQL Server and raster formats like GeoTIFF, through open standards: WMS, WFS (including WFS-T), WCS and WMTS, with OGC API - Features and WPS available as installable extensions. It is written in Java, runs on Linux, macOS and Windows, and is installed and operated by your own organisation. GeoServer is a community project of the Open Source Geospatial Foundation (OSGeo); contributors include GeoSolutions, GeoCat, AfriGIS and Camptocamp.
GeoServer is free software under the GPL licence and has no vendor that hosts your data: you decide where the server runs, for example with a European hosting provider or in your own data centre. That means no dependence on a non-European cloud provider and no vendor-bound jurisdiction. For support and further development you can turn to the community or to commercial service providers.