By Nathan Olivarez-Giles Amazon's Echo speaker is a product like no other, and after nearly 8 months of build-up, it's finally on sale to the general public.Echo is an Internet-connected speaker that Amazon quietly introduced last November, home to a voice-controlled assistant called Alexa who sat listening for her name to be called.Back then, you could use commands like "Alexa, play OutKast" to play music, or "Alexa, is it cold today?" for general info.