It's not Windows only

https://www.hex-rays.com/products/ida/debugger/index.shtml

it's still somewhat expensive though.

Try radare2 - it is opensource, and actively developing - http://rada.re

It also have a book - http://maijin.github.io/radare2book/ Not yet complete, but also evolving. Also you can read our blog http://radare.today/

And for the justice - there is another competitor - Hopper disasm too.

I believe there is a version of IDA which runs on Linux as well as MacOS

IDA is multi-platform. Its pretty expensive, but there's a free version that is definitely good enough while you are learning.