Implementations by Specification

1) Select a specification

OpenGIS Geography Markup Language (GML) - Application Schemas Defining Spatial Geometries 3.2.1

Scroll to Organization:
Top 

interactive instruments GmbH

XtraServer 4.4
OpenGIS Geography Markup Language (GML) - Application Schemas Defining Spatial Geometries 3.2.1 (Certified: 2014-09-29) | Live Test
  Registered: 2014-09-25
XtraServer 4.5
OpenGIS Geography Markup Language (GML) - Application Schemas Defining Spatial Geometries 3.2.1 (Certified: 2015-11-24) | Live Test
  Registered: 2015-11-17

Top 

lat/lon GmbH

deegree webservices 3.4
OpenGIS Geography Markup Language (GML) - Application Schemas Defining Spatial Geometries 3.2.1 (Certified: 2017-05-10)
Official OGC® Reference Implementation | License | Source Code
  Registered: 2016-04-28