The RATP calls the app your “co-pilot; a real journey buddy”. The app offers real-time alerts and offers network maps offline for the metro, RER, bus, trams, ‘Vélib (bikes), night buses (Noctilien), Orlyval and Transilien SNCF (trains on Ile-de-France).
The good news is that as in life, not everything is perfect. Using the RATP app today, I noticed a flaw; the train cars were reversed. Taking line 5 to Stalingrad (line 2), I know from experience that you enter the last car on line 5 to change easily to the Stalingrad line. At Stalingrad you get in the first car to easily exit at Place de Clichy. The app showed just the opposite. No worries, everything else was accurate and they are making an improved effort to make travel easier. Enjoy!