Edited to add: Git. Git is also a thing of beauty. Who knew revision control could be made to not suck? Sure, SVN was a welcome relief from the unrelenting stone faced hell that was CVS, but that's damning by faint praise.
I love git, and use it for all of my projects. But my love for git might also be because I have spent so much time on learning it.
ed went on to influence ex, which in turn spawned vi. The non-interactive Unix command grep was inspired by a common special uses of qed and later ed, where the command g/re/p means globally search for the regular expression re and print the lines containing it. The Unix stream editor, sed implemented many of the scripting features of qed that were not supported by ed on Unix; sed, in turn, influenced the design of the programming language AWK, which in turn inspired aspects of Perl.
And I love AWK too.
I like and use grep. But, as a programmer, I like ack much better than grep.
Ask me what git merge does, or how to branch, or even how to delete a file in a repository (w/o deleting it from your local), or how to revert back to another version, or how to even check out, and I'll say I dunno. I read the documentation, but am still confused. I sometimes feel like I'm dumb because I feel everyone loves git and everyone gets it. Glad to hear that I'm not alone.