Remapping keyboard shortcuts (copy, paste etc) to Alt key instead of Ctrl

Question

Interestingly, it turns out this is almost impossible to do. Remapping ALT key to behave as another CTRL key is not a solution because you lose the ALT key functionalities (some of which are essential, like AltTab).

So how can I get a behavior similar to OSX where CMD key is used for keyboard shortcuts (but also for switching between windows with CMDTAB)?

I know I can assign CTRLTab to switch between windows after I remap ALT key as a CTRL key. But then I lose the real CTRLTAB functionality in some applications, which are also essential like switching between tabs. Basically my CTRL and ALT keys would become the same key and it will be impossible to have two different set of shortcuts for these two modifier keys.

A good solution for me would probably be a way to catch ALTC, ALTV, ALTX, etc. at the window management level and send instead a CTRLC or CTRLV or CTRLX etc. to the focused window. On Windows this was possible via AutoHotKey.

On Linux, I heard about an application called AutoKey but unlike AutoHotKey you have to use a GUI to set the shortcuts. Since I will be writing almost all combinations of Alt manually, I don't want a GUI application do to this. I should be able to configure it by writing a text file.

Is it possible to achieve this either with Gnome or Xmonad?