Listing 4: Query to Calculate the Desired Results, Solution 1
SELECT app, MAX(concurrent) AS mx
FROM (SELECT timeslot, app, COUNT(*) AS concurrent
      FROM (SELECT timeslot, app
            FROM VTimeSlots AS TS
              JOIN Sessions AS S
                ON TS.timeslot >= S.starttime
                AND TS.timeslot < S.endtime) AS TSAPP
              GROUP BY timeslot, app) AS C
GROUP BY app