This object can be seen in Mos Eisley spaceport in Star Wars: Episode IV.
I’ve always wondered what its purpose is. Do we know?
This is a 9000 Z001 landspeeder
The 9000 Z001 landspeeder was a Ubrikkian model commonly used around the time of the Battle of Yavin. It was modified from the 9000 landspeeder, which had been aimed at Ugor customers but had flopped.
At the time of filming, the ship was simply labelled (in the construction blueprints) as "Fourth Speeder". The tag "9000 Z001" seems to have been added later as a retcon.
The Star Wars Galaxy Guide #7 (Mos Eisley) RPG sourcebook also offers the following non-canon info;
From the old newspaper comic strips, it appears to be a "low life droid."