For your lawn? A Springbok rake.

You can hire scarifiers, but be prepared for your lawn to look awful for ages if you do after all the moss has disappeared! (The voice of one who tried it...)

I've got a generic roller one that I bought for about 25 pounds online.

It's good for the initial once (or twice) over - I then follow up with a spring rake to get the thatch into piles.

Hard work either way, but well worth it.

I always follow up with a bit of topsoil and lawn food too.