We're going to close games for some time while we're working on releasing our new client with macOS and Linux support (thank Alyx for that!).
We don't know exactly for how long this is going to be, but expect it to take at least a few days. This is not the version of the client with scripting, which is expected to release in a couple of months.
UPDATE: THE NEW CLIENT AND LAUNCHER HAS BEEN RELEASED. YOU CAN NOW GO TO THE GAMES PAGE AND DOWNLOAD THE NEW LAUNCHER. Thanks!