I've been working on and off on a client-side* SERP rank tracker: https://serpowl.com/

I wanted a simpler alternative to the self-hosted SerpBear tool that I could use and share, so this is the result.

It uses SerpApi (where I work) as the data source for what actually executes the SERP scraping because it's much too complex to have purely client-side, but 100% of the rank tracking portion is client-side.

It's not fully complete and there's definitely rough edges with it, but because of the data source, it supports a large number of search engines right off the bat.