There are a few samplers available which are generic, and work outside DAWs. I don't know if these are really any good, or widely used.

One is Maize Sampler 2 - https://www.maizesoft.com/cms/?page_id=48

Another is the TX16WX sampler https://www.tx16wx.com/shop/

While these don't appear to offer a means of converting one type of Virtual Instrument to another - (such as VST to AU), they might allow generation of both VST and AU VIs from the same set of samples.

These generic samplers are also cross platform - and will run on both Mac and Windows machines.

There may be others, but these are two I have found recently. Whether these are more useful than the samplers inside tools such as Logic or Reaper I can't say right now.