Yes, that is possible, but I believe your users will have to execute the workspaces using the REST API, as it seems the GUI form (where you specify the workspace parameters) requires a login.

I know it is not really without logging in, but:

You can create a Guest user (without password) with Role fme_guest and restrict that role to running workspaces in that repository.

It's not a good option if you don't have unlimited license.

Why is that?

Oops, a password is required when creating a new user. So I would use guest/guest. Still needs a login to FME server. So most likely not what you were looking for.

Another possibility is the single sign-on option as described in this document:

http://docs.safe.com/fme/2015/html/FME_Server_Documentation/Default.htm#AdminGuide/IWA.htm

The fmeguest role provides this sort of unauthenticated access. Each request to FME Server that lacks credentials is first attempted with the guest account. So if the guest account is connected to a role that has permission to use repository 'x', then no credentials will be required. I think the only thing you need to do is give the fmeguest role the read and run policy for your workspace.

A bit more information on the guest account. http://docs.safe.com/fme/html/FME_Server_Documenta...

In FME Server 2019, we now have the concept of 'Apps' which I believe allows you to do just this.