I am looking for recommendations for a simple CMS with the features listed below which are in approximate order of importance.
I generally use Joomla but would prefer something a bit leaner and simpler for some of my smaller clients.
My smaller clients are mostly small businesses and often only need a few pages of information with maybe a slide-show, gallery, a contact page with a location map, and some social networking buttons for sharing their content and linking to their social network pages.
Free and Open Source
Responsive web design as per https://en.wikipedia.org/wiki/Responsive_web_design
Separation of content from design (e.g. via templates or themes)
Ability to run on industry standard shared hosting (e.g. cPanel etc.)
Simple for non-technical users (e.g. website maintainers should not have to learn Markdown etc. to be able to update content)
SEO friendly (SEF URLs, ability to enter page titles and meta descriptions etc.)
Simple updates so that maintaining the CMS is easy
Sitemap (suitable for submission to Google Webmaster Tools) should be automatically updated as content is added / updated
Support forums for the CMS
An established community rather than relying on one or two people to keep the CMS alive
A growing interest rather than a CMS in decline
A small footprint
I realise this may be a tall order but am interested to know if there is anything I have missed, anything new I haven't heard about yet or possibly something on the horizon.
Edit: Added in separation of content from design and extensibility