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what are the most viable native cross-platform gui libraries for clojure(script) as of now?
In Clojure, the big Java-based choices are Swing and JavaFX. For Swing, https://github.com/daveray/seesaw is probably your best bet. For JavaFX there are several wrapper libraries like https://github.com/cljfx/cljfx and https://github.com/fn-fx/fn-fx.
For ClojureScript, the obvious thing is building for the browser, but there are other frameworks like Electron that might be interesting.