LibreArp by The LibreArp contributors is a Virtual Instrument Audio Plugin for macOS, Windows and Linux. It functions as a VST3 Plugin and a LV2 Plugin.
LibreArp is an open-source pattern-based arpeggio generator plugin. It is a MIDI effect (currently supporting any VST3 host on Windows, Mac, and Linux) that takes chords in the form of MIDI input and outputs so-called arpeggios based on the input chords.
Arpeggios are generated using a user-created pattern, which is very very similar in nature to a MIDI pattern in your favourite DAW.