Open source technology to manage WEB portals via WEB browsers.

I am looking for an easy way to design and maintain websites. I've came along DotNetNuke (DNN) technology which once installed allows complete portal and subportal management completely via the web browser. DNN created with Microsoft ASP.NET and is open source. There are multitude of "modules" available - some are free, some are commercial and bunch of tutorials on how to extend and create your own modules.
What I don't like about DNN is it's sluggishness and attachment to Microsoft technologies. ASP.NET 2.0 is very heavy to load and initial wait time is often too long. ASP.NET technology is based in .NET and there is a lot of over-complexity going on under the hood which is reflected in glitches, bugs, frequent failures and other unpleasant issues.

I am looking for technology that would be based on Linux and Apache and would support all these wonders:
- Be installable by a person with an average knowledge of Linux.
- Be extensible with many available modules or so.
- Portal must be fully designable, manageable and extensible through the browser.
- Have wide following and support through forums.
- Be open source.

Thank you.