Q:

Mustache-like templating language with extends?

I like the minimal-ness of mustache-style templating languages - I'm currently using mustache and icanhasmustache, but I've also checked out handlebars and hogan.
However I have a need to for an 'extends' type functionality, to allow a child to reference a particular parent template. I can't find documentation on how extends are implemented in any of the above, but I've seen (from random githib gists) that other people seem to be doing it. 
Note: I'm aware of the existence of includes (sometimes called partials), however these seems to be for a  parent to reference a particular child. That's the opposite of what I'm looking for - the child template in this case is the real 'base' document, the parent merely incidental, so I want the child to control the relationship. 

A:

2016 answer:
If you're using express, the layout middleware takes a layout option which you may find useful. 
res.render('page', { layout: 'mylayout.jade' })

original answer: Very few JS libraries implement 'extends'-type functionality.

Nun is very mustache like, but server only (and no longer maintained)
Swig has extends, but isn't very mustache like.  
Jade has extends and works in the browser, but isn't mustache like 

I settled on Dust.JS, as it uses mustache-like sections, works on client and server, and supports overriding blocks on the parent from the child, giving effective extends support.
See the dust documentation, 'Blocks and Inline Partials' section:
{>base_template/}
{<title}
  Child Title
{/title}
{<main}
  Child Content
{/main}

Overriding the 'title' and 'main' sections from the parent template, keeping the surrounding contents.

A:

I'm looking into Nunjucks, which promises to fix some issues as well as support inheritance.

http://jlongster.com/2012/09/20/nunjucks.html 
https://github.com/jlongster/nunjucks

EDIT:
I have indeed adopted Nunjucks, it's pretty solid so far. One limitation I've encountered is that you can't specify multiple folders for precompiling, but I wrote a script to allow it.

A:

Twitter's implementation of Mustache, Hogan, seems to support inheritance now.
See this recent commit: Hogan 3. Add template inheritance...

