...It originates from the United Nations and is used by many governments as geoportal software.
Active development and discussion takes place on GitHub and OSGeo Discourse. You can also connect directly with the companies supporting the development.
Sourcecode available on github https://github.com/geonetwork/
OSGB Web Map Tools is a set of software code and installation instructions that will enable web developers to produce dynamic mapping web sites using Ordnance Survey map data on the internet.
Gmapper is a PHP class aimed at easing the integration of google maps in web pages. It generates all the JS Code needed for advanced functions such as geocoding and driving directions.
GeoAr intends to be a rich client for WMS and WFS services. It's developed on LZX (OpenLaszlo), so it would serve dhtml(near future) and flash to the user's browser giving the chance of select between them, but having only one server's cource code.