Attached the first minimal stand-alone package containing JSXGraph filter and Geonext plugin for core tinymce in moodle 2.4+
The zip file can be extracted to root of moodle (or to local computer and moved to test server moodle folder. When you login as an administrator moodle should install the plugin and filter automatically - if it does no go to
Site administration > Notifications
From Site administration > Plugins > Filters > Manage filters
You need to enable JSXGraph filter that has two settings:
Default url for JSXGraph is set to http://cdnjs.cloudflare.com/ajax/libs/jsxgraph/0.96/jsxgraphcore.js
Default url for GeonextReader is set to http://jsxgraph.uni-bayreuth.de/distrib/GeonextReader.js
If you want to use local JSXGraph files download them to lib/jsxgraph and change settings.
Plugins > Text editors > TinyMCE HTML editor > JSXGraph (this should probably be Geonext...) has a similar setting as Dragmath plugin: the default setting is that JSXGraph filter must be enabled (globally or in some context) to see the geonext button (and to be able to use it) in tinymce.
To use JSXGraphs on pages of moodle you can either 1) add to Site administration > Appearance > Additional HTML > Within HEAD script tags like
<link rel="stylesheet" type="text/css" href="http://path_of_your_moodle/filter/jsxgraph/jsxgraph.css" media="screen" />
or 2) add to your custom theme (or base theme) layout files tags like
<link rel="stylesheet" type="text/css" href="<?php echo $CFG->httpswwwroot; ?>/filter/jsxgraph/jsxgraph.css" media="screen" />
BUT: not both of these, just either 1) ... or 2)
Geonext applet is using codebase and external jQuery from http://code.jquery.com/jquery-1.8.3.min.js - if you want to change these or want to make geonext plugin use YUI just edit file lib/editor/tinymce/plugins/geonext/geonext.php for your needs.