I've seen that in many blog SW:
- A page where you can find all installed themes in the configuration section.
- Clicking the new theme will select if for use.
- An apply button to refresh.
Thinking about it it will be so easy to do in SS (list the themes directory, click on one to write its name to the config file, click apply to execute the flush=1) that I can't find a reason why isn't one there already.
So far i've checked the modules section and couldn't find anything like it.
Don't know if there is another place to get modules fully supported by SS so i came here to ask.
Yes this is a very popular feature of Wordpress etc. In 2.4 we introduced a SiteConfig panel which you can use to select the active theme but no plans for anything more then that (like previewing, editing etc). Its possible to build a UI for it but not high on the core devs list since the use case for SilverStripe (compared to something like Wordpress) is alot more enterprisey and themes are often part of custom development.
However a module manager API / interface is one of the key features on the roadmap (http://open.silverstripe.org/ticket/3652). Won't be in the 2.4 release but somewhere down the track. During this work theme management would come into the discussion as well.