I'll quote myself from an earlier thread of a similar list of awesome tools; this one deserves to be in it so much:

An ncurses disk usage analyzer: http://dev.yorhel.nl/ncdu

I find this an extremely handy alternative to du, it's somewhat similar to TreeView on Windows.

This tool is a must-have for any on-call sysadmin.

Must-have? Hardly. It's much easier to run `du -sm | sort -n', both of which are already installed everywhere along with coreutils.

Fair enough; "must-have" is a bit strong. But, when I'm responding to a freespace alert on one of 2000-300 servers I've never seen before, the "visualized" data layout is easier to digest than a list of numbers - plus ncdu can drill-down through a directory tree quite nicely.

  vim & emacs

Obscure?

Depends who you ask, I suppose - I come from sysadmin world so none of these are obscure for me. So I'd say they are mainly less popular with the 'average Joe' user base. Judging by the screenshots, the author seems to be coming from Mac world, where GUI editors appear more popular than vim.

Similar to what I thought also with the likes of screen, tmux, curl and the like.

Misleading title. A good portion of tools listed are extremely popular.