I've got Ubuntu on my 2015 MacBook that worked out of the box except dedicated/integrated graphics switcher and the webcam. I also installed Windows which Apple puts out official drivers for. It's just a computer, you can plug in a USB drive and install other operating systems just the same as any other laptop.

It's an older Intel macbook, those are just like most Windows laptops.

If it was one of the newer macbook M's, it would've been quite difficult at least.

battery is cheap and easy to replace though

Mine is 2009 15 inch model. I love it and I have been using it for more than a year. However, sometimes it is quite annoying to use, battery barely holds a charge, it sometimes completely freezes for around 10 seconds (with a lot of ata errors, I am assuming that the SATA cable is the culprit), fan are rattling and Nouveau sometimes breaks itself. The problem is that replacing all these parts would get really expensive, at least if I bought most of them from iFixit.

I just put one down as I walked away from the couch a few minutes ago. :)

I bought it to carry in my backpack in Europe. Super light. Super handy. And inexpensive enough that I did not worry too much of it being lost, broken, or stolen ( which it never was ).