It's not the entire game yet — the tactical battles are working, with the strategic stuff still under construction — but come on, it's Excel.
There's even a story, with the battles set "between the events of XCOM:EW and XCOM 2, where a group of guerilla fighters try to liberate their city from ADVENT control."
As you can see, aside from the visual downgrade, everything mechanical is present, from inventory management to combat moves.
Can't wait to see the strategic stuff! If you want to try it out yourself, there's a download link here.