The OB-Xd, provided by George Reales via discoDSP (and source on GitHub), is an excellent virtual analogue synthesizer emulation. It is not only available as a plugin for several DAWs, but also as a standalone app.

VSTs store individual presets as FXP files, or collections (aka banks) of them as FXB files.

In case you have downloaded an FXB file and want to install it for use in the stand alone app on a Mac, simply place the FXB in
/Users/YourUserName/Documents/discoDSP/OB-Xd/Banks/