Indeed, the "Ju" in "Jupyter" is for Julia!

Out of curiosity, can you have multiple languages in one notebook with the output of one cell, in say Python, be input for a second cell in Julia or R? (emacs org-Babel allows for this -- a feature I use often.)

I just googled it, I don't know a lot about Jupyter, but yes:

http://blog.dominodatalab.com/lesser-known-ways-of-using-not...

http://ipython.readthedocs.org/en/stable/interactive/magics....

To some extent - yes. E.g. you can run R in a Python notebook; just each R cell need to be started with '%%R' (and one need to load rpy2).

See e.g. https://github.com/DELabUW/szkola-letnia-2015/blob/master/za...

Beaker notebook [1] seems to do precisely that, though I have yet to use it in practice.

[1] http://beakernotebook.com/index

Yes, most easily through so-called "cell magics".