Preact is a really great project! I contributed to this myself in a very small way last year to add support for customised built-in elements. I would definitely recommend Preact if you're a fan of React. Synergy is different in a few ways, for example it uses Custom Elements whereas Preact has its own component system just like React. Synergy also separates HTML and JS concerns more clearly, making it a little more like Vue in that respect. Preact and Synergy both share this ability to work "as is" directly from a CDN without any heavy toolchain.