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Get Seasill.

For the Mac and for Windows. The Free plan has no time limit; Seasill and Seasill Pro each begin with a seven-day free trial.

macOS

Version 0.3.0

Not published yet. The first release will be signed before it is.

Download for Mac — soon

Requires: macOS 26 or later, on Apple silicon.
First open: macOS asks once before Seasill may use the system’s wallpaper folder, where your library lives.
Plays: mp4, mov and m4v. Takes webm, mkv and avi too.

Windows

Version 0.3.0

Not published yet. The first release will be signed before it is.

Download for Windows — soon

Requires: Windows 11, or Windows 10 version 2004 or later.
Setup: Asks once for administrator permission: it installs for everyone on the computer, with the service that plays the lock screen.
Also: One wallpaper across all your displays, and the wallpaper live on the lock screen.

Releases are not published yet; when they are, the signed installers are offered here. Your library stays on your computer, and the app talks to Seasill only to check your plan and to load the catalogue. Privacy has the detail.