I like viral the old-fashioned way, by word of mouth. Simple short memorable; problem you solve; positioned among alternatives; intriguing/funny/elegant. Peopl

I like viral the old-fashioned way, by word of mouth. Simple short memorable; problem you solve; positioned among alternatives; intriguing/funny/elegant. People pass it on for its own sake... and if that problem comes up in conversation, "oh I heard about this thing for that".