There have been, and continue to be many companies focused on harnessing wind power for reducing cargo ship emissions. OutSail's (proposed) innovation is putting the sail into a standard inter-modal container form-factor.

Had no clue, excited to explore OutSail’s approach! Thanks for mentioning them

but like what other form factors exist for container ships? nobody thought to put the sails into containers on a container ship before these guys?

I think one of our main innovations is how to make a very tall and rigid sail without a rigid mast. But you're right, once we figured out how we can roll up a 60m sail into a small package it was obvious to put it in a cargo container.

I'm not sure what other options have been considered (by would-be market entrants), but OutSail appears to be the first company that is attempting to package a sail into a 'box'. Some other companies have made devices like kites which were relatively vessel-type agnostic.