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Vulcan is a cheat detection plugin that operates at the packet level. It is capable of detecting combat, movement, and even miscellaneous hacks. (e.g. KillAura, Speed, and InventoryMove). Vulcan also comes with BungeeCord support.
Spartan is an anticheat similar to Vulcan. However, it is notorious for having a large performance hit, and is thus generally not recommended over the alternative options on this page. However, Spartan has recently released multiple features previously locked due to being forced to follow SpigotMC's rules - now providing it with a few extra perks over the competition.
Start by downloading Spartan on their Spigot page, upload the JAR file into your plugins folder, and restart your server! If you want to use this plugin with bungeecord, then you're in luck: Spartan has BungeeCord functionality built-in.
Grim is a bit different: it's a prediction-based anticheat. This means that it simulates all possible vanilla movements, meaning it's also theoretically 'unbypassable'. However, it should be noted that the project is technically in beta, and it does not extensively cover combat checks.
Themis is a well-known lightweight & free anticheat that has been around for over a year. It's currently one of the best check-based free anticheats around! What makes Themis stand out even more is the fact that it actually checks Bedrock players who have connected through Geyser - instead of simply ignoring them like its competitors. (e.g. Vulcan and Grim)
It's best practice to have a test server (even a local one if getting a hosted one isn't an option) to test your anti-cheat configuration before deploying it on your production server. It is important that you are aware of the settings and punishments enabled in your anti-cheat!
Furthermore, as with all anticheats, expect false positives. Please obtain as much information as possible to aid with fixing the broken detection, and then report the bug on each respective anti-cheat's Discord or GitHub.