NUS (short for Nintendo Update Server) is a set of HTTP servers used to serve updates for Nintendo's consoles. For the Wii and Wii U, this server is located at http://nus.cdn.shop.wii.com.
The Wii uses user agent
wii libnup/1.0 for all requests.
Query a list of titles
To query a list of titles, a SOAP request is sent to /nus/services/NetUpdateSOAP, with action urn:nus.wsapi.broadon.com/. The result is an XML structure containing all titles.
Download a TMD
A TMD for a given title can be downloaded from /ccs/download/<titleid>/tmd[version], where titleid is the title ID in hex, and omitting the version uses the latest version.
Download a ticket
A title's ticket can be downloaded from /ccs/download/<titleid>/cetk, where titleid is the title ID in hex.
Any content can be downloaded with a request to /ccs/download/<titleid>/<contentid>, where titleid is the title ID in hex, and contentid is the content ID in hex.