sdf, public Unix shell access
I have mentioned it several times before, but I have been told it deserves an entry on its own.
The Super Dimension Fortress (known also as freeshell) is a public Unix system: that is a Unix system (actually Netbsd running on an Alpha-64) to which everyone (each person in the world having a network connection) can log in and which anyone can use.
From its main page:
Our mission is to provide remotely accessible computing facilities for
the advancement of public education, cultural enrichment, scientific
research and recreation. Members can interact electronically with each
other regardless of their location using passive or interactive forums.
Further purposes include ...