Train routes and schedules - France

For information trains, it is always a good idea to go to the actual company that runs the trains. Which for France is www.sncf-connect.com

And if you are looking for an actual map, there is one here: https://www.sncf-reseau.com/sites/default/files/2019-04/MEP_POSTER_avril2019_POUR_LE_WEB.PDF

Your problem is going to be that RER and trams aren't operated by SNCF. I doubt if there is one app that covers all your options.

Information, itinerary, timetables, maps, concerning public transport in Paris and its suburbs (Île-de-France region) are available here:

https://www.ratp.fr/en/

Apps here:
https://www.ratp.fr/en/apps/bonjour-ratp

Other major cities have their own website and/or application.

The Man in Seat 61 recommends Trainline

https://www.thetrainline.com/

I tried to use them on my last trip, I would get all the way to the pay screen and no further.

Also Rome2Rio is a good planning resource.

Trainline adds a small upcharge to what you would otherwise pay at scnf-connect.com. Someone recommending Trainline over the SNCF site might have a financial incentive to do so.

If you are going to Nouvelle Aquitaine, here is the transportation site.

And here is the PDF map of the train lines in the region.

Tocard - believe it or not, last year I actually paid less on Trainline than I would have on SNCF Direct. I think the difference in prices are due to exchange rate when the tickets are made available.

I used Trainline a lot last year while SNCF Direct was unstable after yet another coding change.

My advice when checking train tickets.... CHECK EVERYPLACE

I have actually found the best deal a couple of times on Rail Europe even when adding in their fees. So you just never know IMHO