I have long enjoyed Martin Gardiner's notes on ridiculous or pointless devices which someone must have been so proud of, or so hopeful for, that he spent money on registering them with the US Patent Office records; there are some examples described here.
Half the fun of these is that their inventors are absolutely serious; these are not jokes or hoaxes, there really are talented and industrious engineers who believe that the world is waiting for their machine for washing animals, or their pillow with breasts, but I have recently discovered a long-established website called Halfbakery featuring equally ludicrous inventions which are not to be taken seriously. In this case the point is that it is, "a community-based ideas bank used by people who wish to propose and develop (not always serious) half-baked inventions. Among many similar such sites (e.g., WorthIdea, ShouldExist, whynot.net, globalideasbank.org, idea-a-day.com), it has distinguished itself by minimalism, irreverence, and a cast of regulars whose takes on suggested inventions are often funnier than the original submission". Wikipedia describes it in more detail here.
An example is the Hullaballoon, a tractor-balloon driven airship:
"A personal airship both lofted and propelled, at a leisurely pace, by a series of balloons tethered to a conveyor belt which moves along the vertically-oriented perimeter of the longitudinal axis of the craft. Each balloon inflates as it moves from the underside of the ship, up around the prow, reaching peak inflation above the center of the ship. The balloons then deflate as they move around and down the backside."