[Symbiote]

I mostly use the command line, so Zsh and its extensive support for tab completion is the most important thing.

rsyn^I e.o^I:/va^Iw^I/ ./ -av --prog^I

autocompletes to

rsync example.org:/var/www/ ./ -av --progress

with alternatives listed if I press tab sooner (e.g. --protocol, --protect-args are shown with the purpose of those flags).

On a local filesystem,

ls /v/w/h/i^I

autocompletes to

ls /var/www/html/index.html

The non-default shell tool I use most often is "jq", a JSON processor. I can interact with a REST API, and answer a lot of one-off queries just in the shell.

I should probably write a tab-completion module for our REST API...