In terms of simplicity Mithril is pretty great. Personally don't love the hyperscript syntax but it can be used with jsx. Also Preact but the mental model is c

In terms of simplicity Mithril is pretty great. Personally don't love the hyperscript syntax but it can be used with jsx. Also Preact but the mental model is closer to React. And Vue can be used from a script tag without a build step too.