The biggest problem for a lot of multiplayer games, even when they're free is pulling in players. To help with that, Pirates, Vikings, and Knights II now supports playing with AI bots.
In the latest update released this month, it adds in bot support for when playing both offline and online. Now servers can fill up with bots and be replaced by players so you're not waiting around for anyone to join. There's also new achievements to do with the bots too, based on how many bot kills you get and one for if a bot manages to dominate you in the game.
Being able to play with bots isn't just to keep the online play active though while servers fill up, it's also a really good way to practice. So now you can learn a bit more about the game before jumping in online. For playing with bots, you currently need to be on official PVKII maps, since they have the Navigation Meshes setup that the bots require to allow them to know how to get around the map.
They also removed the Auto Parry system, so that everyone is now on the same system (previously called Manual Parry) to make it more fair.
Check out Pirates, Vikings, and Knights II on Steam, free to play with no micro-transactions.