A very long time ago there was a free linux version if my memory serves me correctly. But now there is only the paid business versions.
The free versions for these other platforms have pretty large numbers and Avast would also be using the free version to promote the paid versions.
Personally I can't see Avast reintroducing a free version for linux.
Before shooting the messenger, I'm an avast user, using the free version of Avast for Windows for the last 17 years.
