Radio World published this site, which contains on-screen software defined VU meters for monitoring levels on a system or through input jacks. I can see that being useful to those who use a computer as their studio, and feed something like a stream or transmitter, and you can see directly the level that's going out of the sound card to the external device. Once calibrated, like to a scope for 100 percent mod, it should stay accurate.
Now the stand-out program for radio on the site looks like it's the "Level Meter with Digital readout combined with a Sine Wave Test Generator". This baby generates the full range from 1 hz to your sound card's limit, so for lab use you can sweep it and test filter response, IF bandwidth, stereo balance and other things needing a variable oscillator on a PC.