Real mixer

Has anyone come across a real-time mixer app (for free or low cost) that will play two tracks and allow you to mix them on the fly? Audacity makes you set up the volumes separately in the tracks then adds them together into one, but you can’t raise or lower the volume as you record. Very low latency would be good.

Thanks

Win 10
.exe installer

Mixxx: http://www.mixxx.org/