I have an RTL-SDR v4, and a Raspberry Pi.
I am wondering if there is some way to get the ease of use that comes with the flipper zero with the pi.
This is ignoring the packaging, and how small the flipper is. And also ignoring the replaying of signals, as additional hardware would be needed.
You can listen to FM radio with gqrx relatively easily, if you can navigate through hundreds of input boxes.
sudo apt-get install gqrx
Anything more complicated will require some coding knowledge, unless someone already created a library for that specific thing.
There is also a ready-made package to listen to GPS signal, unfortunately it needs an external amplifier and a proper antenna, because RTL-SDR is not sensitive enough for GPS.