The legacy sage notebook is deprecated and not available under Python 3. 
Please use instead the Jupyter notebook: "sage n jupyter" 
Sage Notebook Servers
Note that this list is outdated, though many of these servers are still in operation. The repository for sagenb is at https://github.com/sagemath/sagenb, but it is in very minimal maintenance mode at this point.
Who 
Where 
Why 
Liliana Castañón 
Instituto Tecnológico de Pabellón de Arteaga (Aguascalientes, México) 
Cálculo Diferencial http://www.cursostecpabellon.webs.com/, Cálculo Integral (Calculus I&II) We find Sage the best open source alternative to improve our students' skills and competencies. The fact that you can share your work generates brilliant ideas and new ways to approach a problem. We're planning to expand the use of Sage to giving courses to the teachers, to let them know all the advantages that you get working online. 
Mohsen 
Dept of Mathematical Sciences, Sharif University of Technology, Iran 
? 
Bruce Cohen 
Lowell High School, San Francisco, CA 
first year Calculus class 
KAIST, Daejeon, Korea: http://sagenb.kaist.ac.kr 
Public servers with possible plans for use in courses 

William Stein 
University of Washington http://sagenb.org, http://nt.sagenb.org, http://demo.sagenb.org, http://uw.sagenb.org, http://alpha.sagenb.org 
Public servers for testing, courses, etc. 
Thierry Dumont 
University of Lyon 1 (www.univlyon1.fr), Website (front end to Sage,in french): http://sagemath.univlyon1.fr, Material : 3 sun V40z (24 core), 32GB; Sage version: 4.1; ldap authentification. 
Used "at random" for research, and will be used (next month) by groups of students (about 150 students undergraduate at the same time). Related projects: braille interface for blind students. 
Ondrej Certik 
University of Nevada, Reno http://nb.femhub.org/ 
We provide web access to our finite elements solvers, plus we also use it in the Math 666 course on numerical analysis and Math 282 course on differential equations. 
John Cremona 
University of Warwick, UK https://selmer.warwick.ac.uk/ 
Server for the number theory group, only accessible from Warwick network. 
Robert Mařík 
Mendel University, Brno, Czech Republic 
Server for basic course in Mathematics at Faculty of Forestry and Wood Technology and also for any user from the university. (Not public, behind firewall and accessible either from our campus or via proxy server of our university, full localization to Czech language.) 
David Joyner 
US Naval Academy. It is a "private" server available to anyone inside the USNA's firewall 
For our course sm212 on differential equations (I give graded computer assignments, which they usually do from their rooms at night). Also, one instructor uses the Sage server to illustrate surfaces for a vector calculus course sm221 (for the purpose of explaining surface integrals, etc). 
Willem Jan Palenstijn and Bart de Smit 
Mathematical Institute, Universiteit Leiden (The Netherlands) 
For education use in Linear Algebra 1 and 2 courses and an Elliptic Curves course. For research use by staff. 
Marshall Hampton 
Department of Mathematics and Statistics, University of Minnesota Duluth 
Multivariable calculus, differential equations, linear algebra, and bioinformatics courses, as well as some graduate research projects 
Anders Claesson 
Reykjavik University (www.ru.is), Iceland. It's a "private" server managed by me, available to anyone inside the firewall 
Used mostly by students on various math courses, but also by math staff. 
KarlDieter Crisman 
Department of Mathematics and Computer Science, Gordon College. Used by students on and off campus. 
For use in any undergraduate course that could use it. Lately that has been Calculus IIII, Number Theory, Physical Chemistry, Linear Algebra, and Differential Equations. 
Jonathan 
Chemistry Dept. University of Wisconsin Oshkosh 
For Chemistry 370/371 (physical chemistry Thermodynamics, Kinetics, Transport and Quantum Mechanics). Not required of students, but provided as an extra tool. Also used to provide some practice exercises related to the systems of differential equations involved in chemical kinetics through the "interact" operation. 
Gonzalo Tornaria 
Centro de Matemática, Universidad de la República (Montevideo, Uruguay) 
Graduate and undergraduate math courses in general and for researchers. 
Rob Beezer 
University of Puget Sound, Tacoma, WA, campuswide, campusonly server 
Weekly homework exercises using Sage in Abstract Algebra, Math 433 Classroom demonstrations in Calculus I Math department weekly SageTeXBeamer seminar 
Pablo Angulo 
Universidad Autónoma de Madrid, Spain 
We use the server to share interesting worksheets with the other members of the department. It allows members of the department to try out SAGE without installing it. It also allows all the teachers of Laboratorio to work collaboratively on the worksheets that we will use in the classroom. You can browse some published worksheets: https://lestum.mat.uam.es/pub/ 
Peter Jipsen 
Dept of Mathematics and Computer Science, Chapman University, Orange, CA, 92866 
For our Math 380 Introduction to Abstract Algebra course and Math 270 Computational Math Tools 
Brian Granger 
Physics Department, Cal Poly State University, San Luis Obispo 
Lower division physics courses 
Joaquim Puig 
Faculty of Mathematics and Statistics (FME); Polytechnical University of Catalonia (UPC), Barcelona, CataloniaSpain 
Presently we are using it to allow members of the university (it is behind a firewall) to try SAGE without having to install it. 
Department of Mathematics and Statistics, University of Canterbury, New Zealand: http://sage.math.canterbury.ac.nz 
This server is used in teaching STAT221 (Monte Carlo Methods). Actively used by the class for lectures, labs and assignments. Server is also used in individual and collaborative research. Currently public facing with open registrations. 

maTHμ Research, Tsinghua University, China: http://sage.mathmu.com/ 
Sage promoting subproject of maTHμ  Computing Platform from THU 

John Cremona 
Warwick University, England 
We have a nonpublic server, which can only be accessed from our university network in Warwick 
Richard Bernatz 
Luther College, Decorah, Iowa, USA http://sage.luther.edu 
Used in numerous courses to allow students a moreportable alternative to Maple 
Kursat Aker 
Feza Gursey Institute, Istanbul, Turkey https://sagenb.gursey.gov.tr:7000 ( in English ) https://sagenb.gursey.gov.tr:7000 ( in Turkish ) 
To promote an experimental viewpoint of mathematics 
John Travis 
Mississippi College http://sagenb.mc.edu 
I use this in multivariate calculus, differential equations, calbased prob and stats and linear algebra. Available offcampus as well. 
Society of Physics Students 
Truman State University, Kirksville, MO http://lepton.truman.edu/ 
Accessible only on the campus network or VPN, this server is for general use by students and faculty, including courses and research. 
Miguel Marco, Enrique Artal 
Universidad de Zaragoza https://sagemtm.unizar.es,https://sagefis.unizar.es, https://sagebt.unizar.es, https://sageopt.unizar.es, https://sageinfter.unizar.es, https://sageinfzgz.unizar.es 
This servers are used by teachers in the math deppartment for theirs computer lab classes. There is a separated server for each degree (mathematics, physics, biotechnology, optics, and engineering). Every student has an account, that can be used osage.csd.auth.gr:8080]] 
K. Draziotis 
Aristotle University of Thessaloniki (Greece)https://cryptology.csd.auth.gr:8080 
This server is used by students in the computer science department. 
J. Hill 
University of Colorado https://sage.colorado.edu 
Used by graduate students in the mathematics department 
Past Sage Notebook Servers
Servers which are no longer active:
Who 
Where 
Why 
Jason Grout 
Drake University, Des Moines, IA 
Fall 2009: Math modeling class, Multivariable Calculus class; Spring 2010: Numerical Analysis class, Multivariable Calculus class, and a Calculus 1 class 