Robotek is a freemium turn-based battle game where you mix strategy and chance to summon robotic minions and destructive powers. There is a campaign mode in which you progressively restore humanity's dominion over the post-apocalyptic robot world, as well as matchmade multiplayer gameplay over the Internet.
Although the game is battle-based, the player's actual input is limited to a slot machine system in which they choose the type of power they want to use (minion, attack, or support), then spin for the specific kind(s) of action they will enact. Adding a bit more to the skill side of things, if the player times their first click right they can pick one of the three available actions; the other two are left to chance. If more than one symbol for a particular action appears, the strength of that action is increased. It's quite a bit of complexity in a small space.
The game's freemium aspect is fairly unobtrusive. In campaign mode, every battle takes a certain amount of energy, which premium players can add in campaign mode either directly or through no-cost battles. Regular players can gain energy by winning matches. There's an indirect advantage for freemium players in multiplayer because winning higher-energy-cost matches earns them coins more quickly, and each coin can be redeemed for an advantage in future battles.