SmalltalkHub was getting old and unmaintained. It has been replaced by a static file server during 2020. The public data is still readable and consumable from monticello clients, but modifications are not allowed anymore. Private projects, due to privacy reasons, will not be published in the public archive and will be removed to protect their owners.
What alternatives do I have?
Those wanting to keep using monticello can migrate their projects to other monticello hostings such as http://squeaksource.com or http://ss3.gemstone.com. Those wanting to migrate to git, Peter Uhnak’s git migration tool (https://github.com/peteruhnak/git-migration) automates monticello to git migration in tonel format.