Fonts are a big one and can be a very descriptive fingerprint.
There are applications out there that muddle your installed fonts by making it look like you have a ton of fonts you don't actually have.
But yes, they can see what fonts you have and can tell your OS and other computers you may have used if you've downloaded the same third party fonts for all of them.
If one of those computers was known to be yours at one time, then even if you lock away your identity later on another PC your fonts can give you away.