FrogAA is a free browser MMO about getting to the top of the swamp. You make a frog, you train it, and you spend the rest of your time proving it against other players.
Train at the gym to push your stats, take fights to earn experience, and level into gear and opponents that were out of reach a week ago. The Battle Complex finds you opponents near your strength, the Battle Village is where you spar, and the Mire Arena is a pure ladder: every match pits you against the frog ranked directly above you, and beating them takes their place. The Killing Fields let you raise an army and go to war at scale. The Hall of Ribbits keeps the running totals for level, wealth and karma.
Fishing is its own long game, with species that sit in specific waters and a rare end of the list that takes real commitment. Guilds are where most of the ambition ends up: pool resources, equip your members, and compete as a unit.
Underneath that sits a full economy: jobs and businesses, the marketplace, the bank and stock exchange, a persistent 3D voxel world to mine and craft in, property to buy and decorate, university study that gates what you can do, pets to raise between fights, and a social layer of chat, forums, gifts and chapel weddings.
Free to play, no download, and it runs on a phone.