A few that come to mind, some less known, some more:xargs or parallel: run things in parallel, with lots of optionssed and awk: more well-known but still super useful for processing text files, and faster than Python or Rubym4: simple macro processorscreen: powerful terminal multiplexing and session persistenceyes: print a string a lotcal: nice calendarenv: run a command (useful in scripts)look: find English words (or lines in a file) beginning with a stringcut and paste and join: data manipulationfmt: format text paragraphspr: format text into pages/columnsfold: wrap lines of textcolumn: form...