Note: not my own work, sorry i can't recall where I found this to give due credit. Log in as host and go to host->sql and execute these queries

Question 1: What modules are being used in my DNN instance (excludes admin modules):

select Distinct dm.ModuleName  from Modules m
    INNER JOIN ModuleDefinitions md on m.ModuleDefID = md.ModuleDefID
    INNER JOIN DesktopModules dm on md.DesktopModuleID = dm.DesktopModuleID
    WHERE dm.IsAdmin = 0

Question 2: What modules are installed but not being used:

select ModuleName from DesktopModules where isadmin = 0 AND
    ModuleName not in (select Distinct dm.ModuleName  from Modules m
    INNER JOIN ModuleDefinitions md on m.ModuleDefID = md.ModuleDefID
    INNER JOIN DesktopModules dm on md.DesktopModuleID = dm.DesktopModuleID)