The Domain Hoster InterNetworX (abbr. inwx) offers an XML-RPC interface to access its services. You can even register new domains. Documentation of the XML-RPC API is available for download at https://www.inwx.de/de/download/file/api-current.zip (including examples in PHP & Java plus a PDF describing the API).
There is an operational test environment (ote) to learn and test how to use the API without paying for your orders at https://api.ote.domrobot.com. You need a separate test-account to use it and you can get it on http://ote2.inwx.de.
The available objects to query and modify via XMLRPC can be found on https://github.com/pklaus/python-inwx-xmlrpc/wiki/Available-Objects and here is the overview: