-- Database schema
| app_all : app_id [ INTEGER ] primary_key | app_events : event_id [ INTEGER ] app_events.event_id = events.event_id , app_id [ INTEGER ] , is_installed [ bool ] , is_active [ bool ] | app_events_relevant : event_id [ INTEGER ] app_events_relevant.event_id = events_relevant.event_id , app_id [ INTEGER ] app_events_relevant.app_id = app_all.app_id , is_installed [ bool ] , is_active [ bool ] | app_labels : app_id [ INTEGER ] app_labels.app_id = app_all.app_id , label_id [ INTEGER ] app_labels.label_id = label_categories.label_id | events : event_id [ INTEGER ] primary_key , device_id [ INTEGER ] , timestamp [ DATETIME ] , longitude [ REAL ] , latitude [ REAL ] | events_relevant : event_id [ INTEGER ] primary_key , device_id [ INTEGER ] events_relevant.device_id = gender_age.device_id , timestamp [ DATETIME ] , longitude [ REAL ] , latitude [ REAL ] | gender_age : device_id [ INTEGER ] primary_key gender_age.device_id = phone_brand_device_model2.device_id , gender [ TEXT ] , age [ INTEGER ] , group [ TEXT ] | gender_age_test : device_id [ INTEGER ] primary_key | gender_age_train : device_id [ INTEGER ] primary_key , gender [ TEXT ] , age [ INTEGER ] , group [ TEXT ] | label_categories : label_id [ INTEGER ] primary_key , category [ TEXT ] | phone_brand_device_model2 : device_id [ INTEGER ] , phone_brand [ TEXT ] , device_model [ TEXT ] | sample_submission : device_id [ INTEGER ] primary_key , F23- [ REAL ] , F24-26 [ REAL ] , F27-28 [ REAL ] , F29-32 [ REAL ] , F33-42 [ REAL ] , F43+ [ REAL ] , M22- [ REAL ] , M23-26 [ REAL ] , M27-28 [ REAL ] , M29-31 [ REAL ] , M32-38 [ REAL ] , M39+ [ REAL ] |
-- -- Which category has the highest number of users?

SELECT T.category FROM ( SELECT T2.category, COUNT(T1.app_id) AS num FROM app_labels AS T1 INNER JOIN label_categories AS T2 ON T2.label_id = T1.label_id GROUP BY T1.app_id, T2.category ) AS T ORDER BY T.num DESC LIMIT 1;