Some HP printers, P1102w, have wifi cards, and when not associated with an access point, they will broadcast their own open network. There is no way to disable this except to open it up and remove the wifi card.
I think some Roku models will also broadcast a wifi access point for the remote control to connect to.
Our new Canon all-in-one will optionally run an AP, but it's off by default. I've seen roku APs before but I guess I just assumed they could be turned off or secured.
I think some Roku models will also broadcast a wifi access point for the remote control to connect to.