Use Windows built in WASAPI to capture audio output. Another app, your browser (ex: Youtube) - if you can hear it, you can capture it.
I’m using Reaper in this example, but the same should work with any other similar software.
In “Reaper preferences > Audio device settings > Audio system” , select “WASAPI (Windows 7/8/10/Vista)”. For “Mode” use “Shared loopback (CAUTION)”.
Create a track as usual. In my case, I’m capturing a stereo output:
Hit ‘record’ and start capturing!
Side note: ASIO4ALL
Before WASAPI appeared (ex: Windows XP), you would probably use ASIO4ALL to achieve low latency, if you did not have an audio interface with ASIO. You can achieve the same low latency with WASAPI - no need to install anything.