Interlisp Online provides access to a version of Medley running in the cloud. All that is needed to get started is to create an account - simply an email address and password. Once an account has been created you can log in and start a Medley Interlisp session.
Sessions are preserved for an indefinite time (we haven’t worked out for how long – after 30 days of inactivity?). But it should be good for experimenting and introducing yourself to the environment. Anything you create in the online environment should be treated as transient. If you’re interested in developing and experimenting with Lisp programs then you will want to investigate other options. But, for a first foray, this is a good starting place. The Interlisp/online repository may have more details.