Aliaksei Zholner's Youtube account features various small, clever papercraft engines that he's made over the years, but the latest one, measuring a mere 18 x 13 x 22 mm, is the daintiest, most lovely one yet, and well worth the long hiatus since Zholner's previous outing.
The engine is powered by compressed air delivered by a balloon via a throttled pipe (also made of paper!), and it audibly revs when it's going.
His Youtube page contains this cryptic notation: "Специально для пользователей из стран бывшего СССР: все политические комментарии будут удалены, "особо настойчивые" комментаторы – забанены. Всем мир :)," which Google translates as "Especially for the user of the countries of the former USSR: all the political commentary will be removed, "very persistent" commentators – are banned. Peace for everyone :)" Apparently there is a political dimension to papercraft.