ARA is a way for say a VST to speak to a DAW. ARA is supported by quite a number of DAWs these days.

In the past for example to use Melodyne on a track one would need to play the track and capture the audio in Melodyne. With ARA one can simply add Melodyne as a VST and open up the track for editing. You hear the track through Melodyne.

See https://www.musicradar.com/news/tech/celemony-explains-ara-new-vst-au-rtas-plug-in-extension-506999

This has a fairly good explanation of ARA. Once again a tool for a particular type of use. In this case an interface standard between the VST and the DAW as I understand it.

Tony

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