Karing is a free, open-source client. Its download page holds the builds for every system in one place.
Install a client,
paste the link
We have no app of our own yet. Karing does everything needed and runs everywhere, so that is what we use.
The link appears here once the key is paid for: an unpaid key has none, because it has no access either.
Install Karing
Take the build for your system from the download page. If the site does not open, the same files are on GitHub.
Add a profile
Open Karing and press Add Profile on the main screen.

Import from the clipboard
Copy the link from the Subscription link card, then choose Import From Clipboard. The server list arrives by itself.

Open TUN
Go to the settings and open TUN. Without it only programs that follow the system proxy go through the tunnel.

Turn TUN Mode on
Switch TUN Mode on — now all traffic of the device goes through the tunnel, not only the browser.

Windows: run as administrator
TUN needs administrator rights. If Karing starts without them, TUN switches off again. Set it once: shortcut → Properties → Compatibility → Run this program as an administrator.
Connect
Pick the profile you imported and press Connect.