DarkForestSim lets one simulate the answer to the Fermi paradox, modeling the emergence of radio-emitting civilizations and the blindingly obvious reason we're the only one broadcasting today. The creator, Aristotle Evangelos, offers some thoughts after running it through a few million iterations:
It's possible that we're in a late process [and] that we are very unlikely to encounter anyone else, even though the universe was teeming with civs a few billion years ago, for example. It's also possible that we are earlier in the process, but in one of the large gaps left by a killed civ that was destroyed by another one at the other end of it's range (relative to us). In that case, we are just waiting for the next contact
Our radiosphere is about 200 light years wide, now. The number of star system it rolls into is an exponential curve.