Found it; the package was objed! As quoted from the Github README:
A global minor-mode to navigate and edit text objects. Objed also enables modal editing and composition of commands. It combines ideas of versor-mode and other Editors like Vim or Kakoune and tries to align them with regular Emacs conventions.
If I understand you correctly, most importantly, you would like <tab> to work as <escape> in various "evil states". With emacs, the way I see it, you are offered with more freedom than merely "switching" these two key strokes.
To rebind <tab> for common evil states, you can first checkout with C-h k <escape> while ...
Evil prevents the cursor from moving to the last position in a line when in normal mode, which causes the cursor to be placed inside of the last word on the line instead of after it. This makes forward-word think it needs to move to the end of the line, but because it can't, it doesn't move at all.
To fix this, set evil-move-beyond-eol to t, which will allow ...
Do C-h v evil-want-change-word-to-end RET, then customize that variable from t to nil.
evil-want-change-word-to-end is a variable defined in ‘evil-vars.el’.
Its value is t
You can customize this variable.
Documentation: Whether ‘cw’ behaves like ‘ce’.