What software configuration or VST do you recommend for taking a realtime audio feed and "tune" it to a particular frequency (note)?
Antares invented the Auto-Tune, which is I think what you are asking for. They do a plug-in for Evo, but generally people use the full application.
It can gently or aggressively pitch shift an input note to the closest "correct" note.
This Wikipedia article gives some background, and some example audio clips.
I would also suggest looking at Celemony's Melodyne. I haven't used Auto-Tune for a long time, but Melodyne killed it in the water for me. Notably, when Polyphonic tuning came in. They may be closer now than before. Research!
If you just need a rough match, a lot of DAWs and audio-in synth (FX etc.) have pitch transpose / adjustment. However, the two aforementioned plugins will allow you to tighten the fluctuations in pitch.
You do not say which DAW you are using, but as you mention VST if you are using Steinberg then for real-time operation there is a plug-in that comes with the DAW called PitchCorrect and for non-realtime you have the VeriAudio engine.