You can play osu!(stable) on somtum.fun, a free osu! private server open to players worldwide, with your own osu! install. Your stable scores share one leaderboard with lazer (TumThai) and the old 2008-2015 clients.
Download the Somtum Launcher from the download page (Windows and Linux). It starts osu!(stable) on somtum.fun for you, with our anti-cheat, so your scores are submitted. It also installs and updates TumThai and the old clients.
Prefer not to use the launcher? Start osu!(stable) with the Somtum Patcher from the download page. It connects your normal osu! to somtum.fun and runs our anti-cheat, so your scores are submitted. It also adds a live pp counter.
Make your account in the game, not on the website: start osu! on somtum.fun, register there, then sign in to this website with the same name and password.
-devserver?Starting osu! with -devserver somtum.fun connects too, and you can chat, play and join multiplayer, but your scores aren't submitted: only the Somtum Launcher and the Somtum Patcher run the anti-cheat that lets them count. See How do I connect?
Start osu! normally, without the launcher or the patcher, and it connects to osu.ppy.sh as before.
somtum.fun is fan-run and not affiliated with ppy Pty Ltd.