When I search for "door closer" on Home Depot, I see a wide selection of these devices, the kind that you install at the top of the door, and its function is to pull the door closed.
Is there such a thing that goes the other way? I mean one that will pull the door open to, say, 90 degrees, instead of closing it.
The use case is a shared housing situation with a common bathroom, and our policy is that the door be left open when not in use, but people keep not doing that.
Google did not help.
If changing the hinges is an option (rather than moving them or adding more hardware) then rising/falling butt hinges are available [Example]
These use the weight of the door to force its hingeplate down the central spindle, turning the door in the desired direction. They can usually be fitted as a direct replacement, but since you want the door to fall open, its open position will be slightly lower than it currently is. (Usually these are used to fall closed, which means the door rises as it opens: there's usually some headroom to allow this.)
It may mean shaving the bottom of the door if there's a threshold which needs to be cleared, or if there isn't enough room for the door to fall.
Simple solution for a simple door closer - mount one end to the wall, not the doorframe - then when it "pulls its ends closer" it is pulling the door open. You'll want a solid wall mount (find a stud if it's studwall construction. Use a serious anchor if it's masonry.)
The more industrial door closers (rectangular boxes mounted to the door) rotate a shaft that's connected to the arm linkage - that type probably is adaptable to forcing the door open by changing the linkage around (or putting a left-handed one on a right-handed door.) You'll have to invent "how that works" yourself, as all the instructions are for how to set them to close a door, but I'm tolerably sure it's possible to get there.
If the door swings quite freely, then you can achieve this by shimming out the bottom hinge & shuffling it back a few mm towards the closed side.
Gravity will then mean the door's natural resting state would be open.
To try explain the reasoning behind this - imagine you have a door suspended vertically. It's natural state would always be to point towards the ground; of course.
So the trick is to offset the hinges so that we have a slight hint of this. The lowest point of the swing is 90° to the closed position.
You would, of course, have to disable any latch other than the actual door lock, so it couldn't be closed too far for this to function.
Source of this tip: My own bathroom door. We have a similar 'leave it open' policy, which this method gently enforces. [The washroom has the opposite policy - for which we use a regular door closer]
