Re:OpenChakra is an open-source visual editor for React
by dkrvt on Thursday February 13, 2020 @09:37AM
(#22318017)
You could try WordPress' block editor, Gutenberg [1]. Although not a toolkit it's an extremely customizable UI editor. From within the editor you can create "Reusable Blocks" that are instances of blocks ready to be reused.
[1] https://wordpress.org/gutenberg/