While we do still have 6.5.5 of UBB.threads in the Members Area it does require the same purchase price as you're not only purchasing the software but access to the members area for a year for any updates.
UBBcentral, Groupee, Infopop, Eve, are all run by the same company, yes.
You could use UBB.threads as a CMS/Portal site. It's not quite as feature rich as a true CMS system, but it can be done. You can add navigation links. There is an example script that allows you to see how to create custom pages that will blend in with the forum setup.
Our price is a bit higher than some. But we have some builtin features that others make you pay for, or are not included such as the portal system.
This theme isn't included in the stock download but it can be downloaded from our Styles Download Forum along with a variety of others. Most have a preview of the style as well.
We're very good on our css/xhtml validation. There are some here on this site, but they aren't in the base code, rather coming from this custom style that is in use. Code has been totally rewritten and very easy to follow. We have search engine friendly URLs as you can see from this setup.
We don't have a plugin system, but we do have an dedicated modification site, at
www.ubbdev.com.
The post title not changing is more than likely a bug or a cache not being updated, will need to look at that.
Hopefully I got all of your questions. Let me know if you need any clarification on any of them.
