To shamelessly plug my own (free) stuff, I've been working on Unide [1] as a side project. Currently features only Vaadin components and isn't nowhere near the quality of Hadron or OpenChakra. But you can get a LitElement or plain JavaScript project exported from it, and support for other component sets should be coming in the next version.

[1] https://mjvesa.github.io/unide/