I am looking for an app that reposition my windows and apps, depending on where I am.
I have a MacBook Pro that I use at different places.
Eg, at my home office I am connected to a 35” ultrawide monitor, and have my windows arranged in a special way. At another office I have a 27” monitor with other arrangements.
I am quite sure I have seen apps like this during the years, but I can’t find it now.
Any suggestions? 
Keyboard Maestro will work. In fact, a dedicated package of macros exists for window management:
https://wiki.keyboardmaestro.com/Window_Movers
It shouldn’t be hard to configure them to deploy differently depending on conditions like screen size.
I know that some of the window control apps like Moom, Magnet. Etc, support multi monitor configurations like this.
I am currently using Moom, but have not looked into this kind of functionality so I don’t know offhand if Moom in particular does this.
Note that for these kinds of apps to set up a custom window layout, in general, you need to have all of the needed windows open for the app to work with. If that would not necessarily be the case, you could use a KM macro to activate the needed applications and open the needed windows for each app, then use KM or another app at the end to position the windows.
Bunch from Brett Terpstra is another good choice to handle opening the apps and needed windows and documents followed by Moom to position the windows.
Perhaps you were thinking of Stay?
I’ve not used it so I cannot speak to how well it does or does not work.
What is the best way to get the position and size of windows? I did it several years ago but have changed offices and screens and can’t for the life of me remember how I did it.
I’ve just started to use Moom. It lets you save window layouts based on the kinds of displays that you have attached.
Thankyou guys. I’m currently using BetterSnapTool for windows management. Looked at Moom some years ago, but decided to go with BST ( I think I couldn’t get the keyboard shortcuts as I wanted them in Moom).
And I also have KeyboardMaestro (still on version 9 though), so I should probably start looking at that.
This is the correct answer.
Keyboard Maestro will also do this as mentioned but Stay is an app designed for specifically this.