Cli-junkie brofist! I only drop out of the command line for occasional one-off browser stuff.
Depending on your current familiarity with things, I can't recommend enough simply combing through the tools in coreutils, util-linux, find-utils etc. If you take just three or so a day, by the end of a few months you'll have a solid survey-understanding of what almost every *nix shell has available.
Apart from that, here are some I use and enjoy:
[0]:http://abook.sourceforge.net/ -- Vintage address book; Plays well with mutt
[1]:http://git-annex.branchable.com -- A better Dropbox, and via git!
[2]:https://www.lesbonscomptes.com/recoll/ -- Index and search the contents and metadata of (pdf, word, etc) documents
[3]:https://www.roaringpenguin.com/products/remind -- Vintage and sophisticated tool for doing calendrical stuff.
[4]:https://github.com/trizen/youtube-viewer -- CLI YouTube with all the bells and whistles!
[5]:https://6xq.net/pianobar/ -- Pandora radio!