Watchkin and SafeShare.tv. Another option is to put the video into Google Slides or PowerPoint to display. And a fourth option is to use the browser extension called Quietube. I demonstrate all four of those methods in the following short video.
To be clear, none of these tools are for downloading videos. Doing that would be a violation of YouTube's terms of service and quite possibly infringe on the video creator's copyright. It should also be noted that these tools may not block all pre-roll advertising.