I've been playing with SDR++ by Alexandre Rouma is available for macOS, Windows and Linux. Others, such as SDR#, work well on Windows but mostly I run Linux for ham radio and it's great to find one that works as well on Linux as on Windows. Here it is on Windows:
Even on a low end laptop, the spectrum display updates fast and the receiver works well. (My reception here is terrible though). Here it is on Ubuntu 21.04:
I did run in to a common issue on Ubuntu 21.04. The app crashes on startup. If you run it in a terminal you see this alarming log message:
"Hash collision!!! Fatal error!!"
Apparently it's due to multiple drivers in the soapysdr system. A workaround is to remove them all by running:
sudo apt remove soapysdr-module-*
It's mentioned in the troubleshooting section but I searched for the message with exclamation marks and so didn't find it.
Fantastic to see a high quality, high performance SDR client. I've used it with an Airspy HF+ and an SDRPlay. Others are using it with audio re-direction to receive digital modes.