Two very simple ones here, simple that is if you can weld or have the help from your local friendly welding person/business. The blue one with a sprocket on is composed of a piece of 3/4er by 3/4er Qualcast Concord type tubing for the handle, a sprocket similar to the one I wanted to remove, ( Atco? Ransomes? Webb? it had a left handed thread) plus two short bolts welded into chain sprocket grooves to make a really sound and sturdy job, a piece of bar etc about half an inch thick can also be inserted into the open far end of the square tube for extra oomph.
The second one is simply a bit of 3/4er internal steel tube/conduit with two bigish bolts welded on one end in appropriate places, this is good for undoing other tight things and for bending wire and small pipes etc. again, a piece of bar can be inserted into the end for extra leverage.
Thirdly, but not lastly is a very useful tool I find, it's simply a piece of steel plate about an eighth or maybe a bit more thick, about two inches wide and as long as it needs to be, a foot should be plenty. I cut the slot with a hacksaw about thirty years ago, which then allowed me to insert the ends of single cylinder mower blades into it and gently bend them straight again. How folk can bend a cylinder blade so badly, then carry on trying to cut grass with that clatter going on defies logic, in my book.
The three holes in a triangle enabled me to use this tool to remove a certain Stihl chainsaw flywheel or clutch drum, 041? 050? 056?Sorry I can't remember now.
A slightly better picture I hope.