For detailed analysis in Reaper, I use the JS audio_statistics plug that comes with it. Usually the very last thing on my masterchain.
For VU while mixing I use either VCC if it's the first plug, or PSP vintagemeter set to -18 calibration, and the second metermode (click on the VU-meter once) when it's somewhere in the middle of a chain, which is also free.
Question to the FreeG users. I've tried it yesterday, but whenever I ran an exact same track through it 3 times, it gave me a different RMS in the end every time. This never happened to me with the JS plug, so I think I'm doing something wrong. Anyone know why that could be?