Use & which will run the command asynchronously, so ranger will still be usable while you have the application open.
For example, in your rifle.conf use the following line:
mime ^text, label editor = emacs & -- "$@"
instead of
mime ^text, label editor = emacs -- "$@"
Similarly suppose you want to open an image with gimp then you can press r in ranger to open a list of available applications. The list might look like:
0 | eog -- "$@"
1 | feh -- "$@"
2 | eom -- "$@"
3 | gimp -- "$@"
:open_with
Then use 3 & instead of 3 to open the image in gimp while keeping ranger usable.
Sometime ranger may not be configured to recognize the correct application (for example mathematica). You can still choose that application by typing the name of the application at the prompt :open_with. However to keep the ranger still responsive use the flag f as in:
:open_with mathematica f
(the above method to use a flagf is from here)