I don't know about apps (only used the HVV app, for holding a ticket), but in terms of websites SNCF (at least the English version, the French one is a bit better) is an absolute mess. There is like 3 different ones for starters, one to find a connection, one to buy the ticket and one to find current status/delays.

bahn.de is actually one of the more decent websites in my opinion (definitely better than most rail sites I have encountered).

That said, the biggest problem with rail in Europe atm, is the lack of an integrated ticketing system. Going between places by train is a so much nicer experience than taking the plane, but the ticketing experience is such a mess. As others have pointed out, on SNCF you can't find any international connections any longer (IIRC SJ.se in Sweden still shows connections to Norway and Denmark), on Bahn.de you can find the connections, but can't actually see a price or book a ticket (you are told to go into a station). Train travel in Europe could be a surely awesome otherwise.