I am trying to understand SaaS (software as a service).
What are the different ways of delivering it? We all know using
ssh -X $host we can run software on a remote computer.
Can this be considered SaaS?
Software as a service is a business model, not a technology.
'Software as a service' is a software licensing and delivery model in which software is licensed on a subscription basis and is centrally hosted.
The key point is that it is a way of selling the software. The technology used for actually providing the software remotely doesn't matter; it could be anything.
SSH -X could, in theory, be used to deliver the software in this model. It is a way of allowing software to be executed remotely. But this isn't typical. Most of the time SaaS refers to web applications.
SaaS is a business term for the delivery of software. "Service" here is being used in the business sense (plumbing service, roof repair service) rather than in the technical sense (HTTP service, SSH service).
To directly answer your question, you could charge a fee for someone to access an X11 host (to which someone could connect to via
ssh -X). You could then say that you were running a SaaS business.