Does Reaper have a limiter?
There are also several actual limiter effects in the JS effects library that comes with Reaper. Just open your FX browser and either search "limiter" or navigate to the JS section and scroll down a bit.
What does the limiter do?
A limiter is a tool for signal processing (like mixing music) that applies a type of dynamic range compression. That means that it can take an input signal, evaluate its amplitude (volume), and attenuate (lower) the peaks of the waveform if those peaks reach and exceed a threshold value.