I haven't a clue. The only thing I can think of is a small two cycle engine right above the shaft.
the jug is on the far side .. looks like a modified Seagull outboard engine.
I'm with Silvius; that looks like a modified British Seagull.
I think it's a homemade self-propelled lawnmower.
'Looks really well made for homebrew. I don't think it's self-propelled. The vertical shaft goes through a height adjusting clamp, and that's it. 'Doesn't look like it connects to the wheels up front or the roller in the back.
OSHA would like to have a word with the builder.
It has to be something like that...