Playing games

Special setups

Two people on one Mac

Each person sets Superposer up in their own macOS account: open Superposer once (it installs its components for you, about 1 GB) and turn on Steam integration. Everything is per person: your own Steam (Mac Steam lives in each user's home folder), Windows mode and Superposer's tools inside your Steam, the new-game watcher, the Windows runtime, the games' Mac apps, your settings and the list of changes. Only Superposer.app is shared: everyone's Steam runs Superposer's tools from it, so keep it in Applications while anyone uses it.

• One Steam at a time. macOS runs one copy of Steam per Mac: while Steam is open in another person's session (fast user switching), yours won't start ("You can't open the application Steam because someone else is using it"), and Superposer's Play says so. Ask them to quit Steam, or switch to their session and quit it. Setting up, turning integration on or off and uninstalling only need your Steam quit.
• Uninstall Superposer removes only your own setup, and names the other people on the Mac: if any of them use Superposer, leave Superposer.app in Applications.
• A Steam library you share (an external drive, or a folder in Shared):
  • On an external drive with Ignore ownership on this volume (how macOS sets up external drives), both of your Steams use the same game files and the same Windows environment for a game (Steam keeps it next to the game). Local saves inside it are shared; Steam Cloud saves stay with each Steam account. Uninstalling Superposer removes only the Windows environments your own Superposer made; uninstalling the game in Steam removes it for both of you.
  • Where ownership is kept (the Shared folder, or a drive with that option off), Windows games only run in a Windows environment you own: a game whose environment the other person's Superposer made stops with a message naming them. Install your games in a library of your own, or turn Ignore ownership on for the drive (Finder › Get Info).
• Games on a second library (any external drive) use Valve's Steamworks files from your main library, which copy-protected (SteamStub) games such as Banished need.

Steam Families (borrowed games)

Games you borrow from your Steam Family show up in Superposer's library like your own and get the same choice (Mac version, or Windows version through Superposer). Steam installs them, checks the licence when you press Play, and then starts them through Superposer like any other game; Superposer doesn't look at who owns a game. Steam Cloud saves of a borrowed game are your own, and Steam's family rules apply (one person plays a borrowed game at a time). If the game has a licence agreement, Steam shows it the first time you press Play.

Steam offline mode

Steam › Go Offline works with Windows games: Superposer's Steam support talks to the offline Steam, copy protection (SteamStub) accepts the game, and Steam loads achievements and stats from its own copy. Achievements you unlock offline are kept by Steam and sent when you go back online (Steam's own behaviour), and Steam Cloud syncs then. Superposer itself needs no internet to start a game.

What was tested

On a test Mac (macOS 27, 2026-10-08), with Banished and a game borrowed from a family member: