Commands — I usually will ship with Rectify https://github.com/andypike/rectify. It's a great layer for my controller to handle request contexts. You might think this is a glorified service object but I'm not a fan of service objects unless they do just one thing (and are allowed to loudly fail).
Components — https://viewcomponent.org/ I'm not incredibly sold on them but they do clean things up.
Forms — Rectify has this shipped but it uses Virtus which is quite old and hasn't been touched in many years. Shipping my own similar is usually something like https://gist.github.com/joshmn/39eb6f302650e09743387710591ab.... Not all of my form attributes will map directly to a model, but I want my form helpers to actually help me so I need some sort of object that _can_.
Inputs — I'll extend SimpleForm inputs (something I can't live without) to DRY up my forms.
All together, this is typically something like this (the form and command pattern, at least): https://gist.github.com/joshmn/65cfbccc6c64abe6d463ba9708b00... (not tested)
There's usually also an `admin` directory since I also usually ship with ActiveAdmin or Trestle. I've fallen in love with the latter after making it behave more like ActiveAdmin. When I need to drop out of its usual constructs I'll just write a custom controller, but for the majority of administrative stuff I can get 95% of the way there with the DSL of either/or, freeing up time for domain-specific problem solving.