If you go looking for Koush's Vysor today, you won't be able to find it. Koush has announced that he had to pull the screen sharing app because of codec licensing. Despite being more or less ubiquitous, the H.264 codec isn't a free standard. Koush was contacted by MPEG-LA and told he'd need to license the decoder in Vysor for $0.20 per user. Koush opted to pull the tool from the Chrome web store instead, but he's on the hook for previous downloads.
Vysor is free to download, and at $0.20 per user, that could mean a big bill for the codec. As it stands, he's still being asked to pay for all the previous downloads—so, some non-trivial amount of money. Koush is looking into a solution, but switching codecs might not be an option. Unfortunately, H.264 is supported on all devices, whereas the open VP8/9 is only supported on some. It's possible Vysor will come back as a paid download, but Koush isn't saying yet.