Your description of AT is completely off. I'm an active user of RT and Asset Tracker (AT). It's not a toolkit at all, it's a clean modification that adds an 'Assets' link in the nav bar where you hold assets. From there you create and manage custom fields and custom field values from within the standard locations of RT. At no point must you know a URL to do anything in RT or AT. There are simple or complex searches, linking assets to others (depends on, requires, etc) is simply typing a few letters into a box to search on, then choose the appropriate action from a dropdown box.
Unfortunately there have been no releases of AT in a while, but it still cleanly applies even to the latest version of RT. It does have a new home for its code on google code and is getting updates, just not a new release for a few years.