It's funny this is coming up as a topic just now. Only today was I researching the web to get my head around how "Railteam" in Europe works. The simple summary is: when you have a status card of one of the member railway companies of Railteam you have access to the lounges of member companies. It's like an airline alliance with lounge access privileges for status members of all member airlines. Member railway companies are Deutsche Bahn of Germany, SNCF of France, SBB of Switzerland, ÖBB of Austria, NS of the Netherlands, SNCB of Belgium, and Eurostar covering the France/Belgium/Netherlands-London route as well as routes between Paris, Brussels, Amsterdam, and Cologne.

However, that is the simply summary. In practice it's much more complicated, but there is little information about it. Some of the rail companies require an international ticket, others any ticket, others no ticket, others don't let you in at all, and some other restrictions and special rules for specific extra lounges.

I was hoping to find some information here.