amsynth by nickdowell is a Virtual Instrument Audio Plugin and a Standalone Application for macOS and Linux. It functions as an Audio Units Plugin, a DSSI Plugin, a LV2 Plugin and a Standalone Application.
AmSynth now has 5 soundbanks included (each soundbank contains 128 patches) and you can hear some examples on my website here: http://amsynth.com/amSynthDemos.html
In order to use these patches, however, you need to use the developer's version, as it has a series of additional features which will not work on the older version. The new version can be obtained by adding the developer's channel to your repositories. The link is on the amsynth.com website.