There's KFXInout I think it was called, for the conversion of kindle books together with dedrm
I tried it a couple of times when a book wasn't available on any platform beside amazon. Getting those books to open at all was a pain in the ass and didn't always work the same way so I would recommend only using that as a last resort anyway.
Aside from those 2 I don't think I use any plugins.
Keep in mind that Autoshelf is not a calibre plugin but a mod for kobo ereaders
I've really got to try those arr programs out some time. I think I had a docker container with one set up once but got confused and decided to not use it