Reversing audio is usually done NOT in real time—you must record it and then flip it around and line it up with your music track. Reversing audio in a DAW is a simple task but having it happen (more or less) in real time in a plug-in is what is new here!
United Plugins' JMG Sound’s Mirror is the first "reverse negative delay" plug-in. Mono or stereo audio is recorded into a buffer then it is played back in reverse. By looking ahead in time of the "play head" in your DAW, you'll have your dry audio (in any blend) along with reverb mixed together as backwards audio.
I used Mirror in a Pro Tools session on a big-sounding drum loop but first I had to set the Time parameter for the 1/4 buffer size to temporarily store the audio to be reversed. This worked fine for my loop that is right on the grid at 75 BPM. On the same song, the main acoustic guitar's finger picking part sounded awesome reversed with a little backwards reverb.
I used Mirror without Negative delay and there is no latency and the reversed audio plays right after the original dry like any reverb. If you want the reversed reverb to play from the start, use Negative delay if your system has enough delay compensation or just record it beforehand and slide it into sync.
I used Mirror on drums, guitar tracks, reverb returns, even bass tracks and I found plenty of subtle uses for choirs and keyboard pads.
JMG Sound’s Mirror is available as AAX, AU, VST, and VST3 plug-in that's downloadable for a time-limited introductory of €22 with a regular price at €69.