I agree with people proposing Linux over Chrome OS, but I have to stress that old version of MacOS are not usable.Even a really old version of MacOS is better then the most current ChromeOS. This is pointless.
I have an old black macbook whose hardware is just fine for browsing, documents etc. (2 core 2,4ghz, 4gb ram, brand new ssd disk).
But because Apple restricts me from upgrading to a new MacOS version, I cannot use my Mac.
Every website I enter with Safari is unreachable due to my certificates being out of date, and I cannot even update Safari to the latest version, so it's stuck there.
Can't install Chrome either, since I cannot enter any websites, as already mentioned.
On the other hand, the same macbook runs Elementary OS (Ubuntu flavor) just fine, and I guess Chrome OS too (I'll have to try).