[Enthusify]

Originally Posted by imported_stefan

Is there a backup strategy for installing it locally on my server if you don't want to work in the future?

Yes.

Originally Posted by imported_stefan

I also like the idea never to uprade my software because its installed on your server but in this case I open my server totally for you, right?

It might help to show an example. Here is the Enthusify plugin powering the marketplace on this site:
http://elightbars.org/classifieds.php
The plugin "injects" a copy of each listing into a designated subforum(s). Thus, you end up with a back-up copy in thread form. If you have the plugin installed, the thread version of the post and the Web 2.0 version of the post in the plugin sync. When an item sells, both versions update. Here is that same marketplace in thread version:
http://elightbars.org/f87/

The Enthusify marketplace plugin for vBulletin can route the thread version of the listing into corresponding subforums depending on the category assigned to the listing for larger sites with marketplaces broken into different subforums.