Playtime Booster
The Steam Playtime Booster feature is similar to Idle Master Extended and allows you to idle one or more games manually to boost their total playtime.
You can idle a maximum of 32 games at once. This is a Steam limitation
Steps
Click in the sidebar
Click beneath the game image to begin idling the game
Click in the sidebar to view the games you are currently idling
Additional Information
When idling games with Playtime Booster, external SteamUtility (idle) processes will be opened to interact with the Steam client and imitate game processes. These processes will be closed when the game is no longer being idled.
If you have previously used Idle Master Extended by Jonas Nilson in the past, the Steam Playtime Booster is a great alternative, as it does not require any additional setup or configuration. Simply select the games you want to idle and start boosting your playtime!