Version managers install runtimes you tried once and kept forever

Version managers make trying a new runtime free, which is the point and also the problem. Each install is a complete runtime, they are never removed automatically, and after a few years a Mac holds several of everything.

List what is installed

du -sh ~/.asdf ~/.sdkman ~/.local/share/mise ~/.pyenv ~/.rbenv ~/.nvm \
  2>/dev/null | sort -h
asdf list 2>/dev/null; sdk list java 2>/dev/null | head -20; mise ls 2>/dev/null

Find what your projects actually pin

cat ~/**/.tool-versions ~/**/.sdkmanrc ~/**/.python-version \
  ~/**/.ruby-version ~/**/.nvmrc 2>/dev/null | sort -u

That is the list of versions something on your Mac requires. Anything installed and not in that list, and not your default, is a candidate for removal. It is usually most of them.

Removing cleanly, per tool

The download archives underneath

Most of these keep the archive they installed from as well as the installed runtime, in a downloads or cache folder inside their directory. Clearing that costs a redownload only if you reinstall the same version, which is rare:

du -sh ~/.sdkman/archives ~/.asdf/downloads ~/.pyenv/cache 2>/dev/null

Why this is worth doing once a year

Runtimes are large, individually forgettable and collectively significant. On the Mac these guides are measured on, nvm alone held 4.5 GB across eight Node versions, and that is one tool of five. The audit takes ten minutes and does not recur if you remove versions as you finish with them.