Lit-HTML is a templating system that's baked into Lit-Element, which is basically the successor to the Polymer framework. It simply uses JS template strings, with a few little niceties in the binding syntax to allow for things like setting properties rather than attributes, adding/removing boolean attributes, and defining event handlers inline. It lacks two-way data binding, but we use "data" elements as a centralized data store. That store provides a master state object that's passed down to every component on the page - though frequently it's just a sub-tree of state that gets passed down. If a component receives some input and needs to update its state, it fires off an event with the updated value, which has a corresponding handler in the data element. That handler taps into a functional pipeline we've built to handle function composition, passes the information down the appropriate pipeline, and the master state is updated appropriately. At that point the data element fires a "state-changed" even that basically everything listens for, and whoever cares can then update their own little bit of state from the master store (typically one line of code).