WorkManager API allows for deferable background work and was released in 2018. It was aimed at  performing work even if your app has scheduled it and the app process has died. The main use cases for Work Manager include uploading logs, taking backup etc. WorkManager is a part of Jetpack, so it is compatible with all older versions of Android. An app can schedule any deferable work to the WorkManager. The Android OS stores jobs from apps on behalf on Job Scheduler on the current versions of Android. The Job Scheduler wakes up WorkManager at the scheduled time to carry out the job. One thing to note here is that the jobs are carried out at best effort basis i.e. the execution of job may be delayed if the system is busy with other priority tasks or has high system load. If you want the work to be done at exact time, use AlarmManager.  

The jobs scheduled by WorkManager are persistent and survive app crash or system reboot. Though, if you force stop an app or uninstall the app, all the jobs scheduled by the app on WorkManager automatically get cancelled. You can configure to perform work only under specific condition using android WorkManager Constraints. You can specify constraint which tell the system, when the work should be carried out..

In earlier versions of Android, instead of Job Scheduler, the WorkManager would use GCM Network Manager if Google play services was installed. In absence of Google Play services it would use Alarm Manager and Broadcast Receivers to carry out the same functionality. As part of the app, WorkManager earlier used to get initialized during app start up. If your app was using WorkManager, this caused an additional 10-20 milli secs of app start up time that went into initialization of WorkManager. In the current versions, WorkManager supports Dynamic initialisation, which has reduced its impact on startup.

Due to restrictions introduced in Android, JobScheduler allows only 10 minutes of work to be done in background, after which it automatically gets stopped and if you restart it will start from beginning. But to the developers delight,  you can now get work done through WorkManager as a foreground service. This flexibility was added to WorkManager because there might be a scenario where in the app is in foreground and wants to get some work done but the JobScheduler does not immediately schedules work as system is busy and later your app goes in background and this work may be get postponed indefinitely. When running as a Foreground Service, if constraints are met, then the work starts getting executed immediately without even contacting Job Scheduler.

WorkManager allows use of primitive data types by workers to report progress. It is helpful in use cases like when you are downloading files and you want to report back how many files have been downloaded so far.

JobScheduler has a limitation that it can schedule at max 100 jobs at a time. Work Manager  allows app to go beyond these limits by doing the heavy lifting to provide the ability to schedule many more jobs than this limit.