Not useful on its own but https://sablierapp.dev/ was really useful for me in getting back resources from some of the heavyweight containers I use. For those unfamiliar with it, Sablier can stop containers that go idle and then spin them back up automatically when a request comes in. It requires Traefik, NGINX, or Caddy running always so it could complicate your server but for me I couldn’t do without it.
It probably would work well with those as long as the startup time was quick (my containers come up almost instantly) and the initiating clients can handle a bit of latency. I didn’t notice any hiccups in my use at all.