It's not too difficult to figure out how to get Pluto's API to cough up the stream URLs, if you're the kind of person that knows how to use the developer tools in your browser. You can do similar things with Stirr and Tubi. Roku and Samsung also don't bother to encrypt their streams, but I don't think they have websites where you can watch them, so you'd have to tear apart one of their apps or get their list of channels from someone else.