Of course, you could use a version management tool like nvm/rvm/asdf etc, but I think containerisation is also a neat alternative, as you would be able to use multiple versions for languages/tools and libraries within those languages for which a version management tool doesn't exist.

Why would you be doing development as root?

Personally I would use virtualenvs with Python to solve that problem you described.

there's still system level packages that you might need, which may come into version conflicts among each other.

note: me too I default to virtualenv for local development, however there are usecases where this becomes insufficient.

I think root refers to the main system environment, not the privileged user.

Let's say you maintain or occasionally code several big webapps in Ruby. One uses Ruby 2.4 and Ruby-on-Rails 3.2, another uses Ruby 2.6 and Ruby-on-Rails 5.2, and the last one is bleeding edge using Ruby 3.0 and Rails 6.1

Having all versions of you language and framework installed top level is a huge pain in the ass, since they inevitably will interfere with each other. Having separate containers with all necessary dependencies in it for each app is a lot more manageable.

rbenv actually solves this quite well. You can set a project-level version in a .ruby-version file, and each lang version has its own gem cache

Yeah. I have over a dozen Ruby on Rails apps on my development machine, targeting a variety of Ruby and RoR (and other common gem) versions. I'm not aware of any problems anyone has experienced in recent years, since everyone has moved to rbenv. We used to see issues with rvm.

I don't use docker with any of these projects. They're mostly legacy for us at this point and are shipping to EC2 instances directly.

Our more current projects do use Docker, however, and we're doing development along side of Docker in those instances and that seems to be working fine for us.

I do appreciate that a dev container would / may be a better approach to this for other reasons and especially, potentially, other languages and ecosystems, though.

I used to work at a company where I'd write and maintain multiple microservices, so I was dealing with dozens of small and big ruby applications across different language versions and different frameworks and dependencies. It was two years ago, but I did experience a ton of issues between different versions of Bundler and rake and rubygems. I'd absolutely go full docker if I was still working there.

I work with several programming languages, its easier to make the problem language agnostic.