Since activeCollab 2 you can choose the URL that users will be redirected to when they logout.
By default, they will be redirected back to the login page, but if you provide another location (a certain page of your website, for example) then users will land there instead after they logout from activeCollab. To set-up the landing page up, open Administration > General settings page:
At the bottom of the General Settings page there is When User Logs Out switch:
When you make the changes and submit the form, try logging out to confirm that everything is working as it should.