Sliding stepladder. By Che Binh Dan. 2:07 video:
https://www.youtube.com/watch?v=y5uOV4KlBBw
Previously:
https://www.homemadetools.net/forum/...071#post157266
https://www.homemadetools.net/forum/...494#post117152
https://www.homemadetools.net/forum/...584#post151593
https://www.homemadetools.net/forum/...434#post150970
https://www.homemadetools.net/forum/...039#post149277
https://www.homemadetools.net/forum/...760#post124166
https://www.homemadetools.net/forum/...2215#post75959
https://www.homemadetools.net/forum/...519#post132193