Caddy is pretty nice, I believe Coolify uses it as part of their self-hosted open source PaaS model. Just out of curiosity, are there any alternatives in Rust? I think Pingora is one, as well as River which is built on top of it [0], but I'm not sure how widely used the latter is as a Caddy replacement.
As far as I know only NGINX Unit[0] might be considered a viable-ish real alternative to Caddy. But other than that nothing comes close to Caddy's ease of use and versatility. You get a lot of stuff and there are heaps of community modules for it, the only downside last time I checked was increased memory usage compared to standard nginx and slower performance as a reverse proxy.
Depending on your setup the fact that you have to choose between Caddyfiles (which are easier to reason about than nginx config files) or the REST API for configuration might be a downside to some people. There's a chance I might be wrong about this one though.
But to answer your question directly there are no real alternatives in Rust as of now.
AFAIK traefik is written in rust. I don't have any experiences with it though. I only had a brief look when setting up some personal project, but ended up going with caddy, because traefik seemed overkill for my requirements.
[0] https://github.com/memorysafety/river