Software Technologies that I MUST Learn

Dan Weinreb explains what this list is about further down in the comments:

What I mean is, my friends and co-workers come up to me and say, oh, Dan, you’ve just GOT to learn about XXX! I sigh and add it to the list; if this guy said it’s cool and important, then I suppose he must be right, since I respect him so much. But when on Earth will I find the time?