Is it possible to remove the /forums/ subfolder from URLs? My website is http://wearabletechforums.com and the /forums subfolder for URLs is a bit superfluous.
I don't understand. The period is added by xenForo before the ID of the forum in the database. If I change "Replace With:" to "activity-trackers/" the URL will not be correct.
I don't really follow what you mean by the "URL will not be correct". Since you're changing the URL, you can change it to what you want (subject to constraints); leaving the number will provide literally no benefit once the URL is changed.
The constraint is that you can't have certain characters before the first "/" -- generally, you should stick to a-z, 0-9 and - .