There is a desktop app for Windows, macOS and Linux. It runs the same client the browser does, in its own window, and it remembers every server you belong to.
Pick the installer for your system on the download page.
Windows and Linux update themselves after that. You get a menu item and a prompt when a new version is ready.
macOS does not. Updating there means downloading the new version yourself. The reason is in the warning below.
Open app.outpost-chat.com instead. Same client, nothing to install, and it works on a machine you do not own.
Install the app if you want it in your dock, if you want it to update itself, or if you would rather the client come from your own machine than from a website.
Every Outpost server is its own community with its own account. See Getting Started for what that means.
The app keeps a list of the ones you belong to. Switch between them from the name at the top of the channel list. You stay signed in to each.
Screen sharing works in the app on all three systems. It was broken until v0.4.0, so update if you are on something older and the button does nothing.
Five of them, including a light one. Signal Fire is the default, warm ember on deep slate, the same palette this site uses.
Pick yours in user settings, Appearance. See Themes & Appearance.