The Editable Web is free and all it's source code is available
here. You can do what you like with it, no conditions.
(1) You'll need a webserver with PHP support. Edit your .htaccess file to protect the "editable.php" file that you're going to download. IMPORTANT: this security step is vital -- but once you've done it, you're perfectly secure. You might find it useful to read the tutorial on .htaccess security.
<Files "editable.php"> <Limit POST PUT GET> require valid-user </Limit> </Files>
(2) Download editable.zip (51k, version 0.1), unzip it, and put the contents in some directory named "editable" on your webserver.
(3.1) There are three ways to make an editable page. First, if you have Firefox and Greasemonkey, click on this link to install the Greasemonkey script into your browser: editable.user.js. This way, all pages will be editable.
(3.2) Alternatively, in any web-browser, open up editable/index.html in the directory you unzipped to. From here you can browse your website and click the "new page" button to create a new editable page.
(3.3) Alternatively, to make an existing page editable, just
add a script
tag to its header (again, pointing to where you unzipped to).
This option is best if you're setting up a website for a non-technical
person, so they can edit it without needing Greasemonkey:
<script type="text/javascript" defer src="/editable/editable.js"></script>