What is ARA? It has come up in this issue (in my review for NoiseWorks' VoiceAssist), and we've mentioned it in the past. I think it's an important concept to understand in digital audio production. Basically, think of this as two different computer applications working in tandem to supply audio files to the DAW (digital audio workstation) that have been externally modified yet can be continuously updated. Think of it this way: You tuned a vocal track outside of your DAW and then rendered it. Then you hear one spot where the tuning app went buggy on a note, and it's not cool. This is going to require a bit of workaround. If I’m using Celemony's Melodyne via ARA in my Avid Pro Tools session, I can quickly jump over to the ARA window and fix the issue. No time spent sending a track to an outside app, no weird processing, and no rendering (unless you want to totally lock it in).
At this point (as far as we know), the DAWs that feature ARA implementation are Avid Pro Tools, Fender Studio Pro, Apple Logic Pro X, Universal Audio LUNA, Cakewalk by BandLab, Reaper, Acoustica Mixcraft, Tracktion Waveform, Boris FX Samplitude, and Steinberg's Cubase and Nuendo.
Now, 2018's ARA2 is likely the version you are using. It introduced more undo capabilities within your main DAW, better multitrack support, and tighter syncing. Synchronization is something to seriously consider though, as I've never seen a warning panel telling me my ARA tracks are not reintroduced back into my session fast enough. Think about the phase issues that could happen with two applications working in tandem. But man, the benefits so far are amazing… 
