Just-the-core
A web page can be a simple HTML file. To open an empty file and an HTML editor for it in your current world do:
Creating a webpage
In the following it is explained how to build static web pages using Lively that themselves do not depend on Morphic. If you are just interested in a minimal project setup, see users/robertkrahn/just-the-core/.
1. Open a world menu, choose Run command...
2. Enter "iframe" and choose the command open url in iframe
3. Enter a URL pointing to a non-existing file on the current Lively server, like
4. An iframe Morph will open. Open a menu on it and click on Edit page
5. The editor that appears allows you to edit the HTML source of that file. When you save (Command-S / Control-S), the HTML document at this location will be created and the iframe Morphs in your Lively world will update.
Loading Lively core
Loading the Lively core system can be done by making sure that a few Lively scripts are loaded. This is normally done automatically during the bootstrap phase.
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="http://lively-web.org/users/robertkrahn/just-the-core/pre-lively.js"></script>
<script src="http://lively-web.org/core/lively/lang/Object.js"></script>
<script src="http://lively-web.org/core/lively/lang/Function.js"></script>
<script src="http://lively-web.org/core/lively/lang/String.js"></script>
<script src="http://lively-web.org/core/lively/lang/Array.js"></script>
<script src="http://lively-web.org/core/lively/lang/Number.js"></script>
<script src="http://lively-web.org/core/lively/lang/Date.js"></script>
<script src="http://lively-web.org/core/lively/lang/Worker.js"></script>
<script src="http://lively-web.org/core/lively/lang/LocalStorage.js"></script>
<script src="http://lively-web.org/core/lively/defaultconfig.js"></script>
<script src="http://lively-web.org/core/lively/Base.js"></script>
<script src="http://lively-web.org/core/lively/ModuleSystem.js"></script>
X
After these scripts you can define an entry point to your application using the lively.whenLoaded(function() { ... }) call. Once the system is loaded you can use Lively's extension of Functions, collections and workers. You can also use Lively's module system to load additional Lively code or external libraries. For example, to write code that depends on Lively's data binding mechanism you can add to your newly created HTML file:
<script>
lively.whenLoaded(function() {
    lively.require("lively.bindings").toRun(function() {
        var obj = {};
        lively.bindings.connect(obj, 'attribute', console, 'log');
        obj.attribute = "A value";
        obj.attribute = "This should appear in the console";
    });
});
</script>
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A full example can be found in users/robertkrahn/just-the-core/. example.html (show source) loads the required core code, as well as a small non-Morphic Lively module that defines the red widget.
Example
With this setup you can conveniently work on a non-Morphic HTML project but still use Lively and the Lively tools for development. Note that you can also directly evaluate code in the context of that HTML page. use the Open workspace menu option for this.
To connect your Lively world and tools to an arbitrary HTML page (that doesn't have to be run inside an iframe) have a look at lively-2-webpage.