If you've played Catan to death and want something with the same spirit (trading, building, resource management) but different mechanics, here are 7 options you can try without spending anything.
Carcassonne
Instead of hexes and dice, you place terrain tiles turn by turn and compete for cities, roads, and fields using your meeples. Like Catan, it's about progressively building the map and racing to claim the best spots before your opponent does.
Ticket to Ride
Swap settlements for train routes: you claim connections between cities and race to complete secret tickets before everyone else. It's lighter than Catan but keeps that constant competition for space on the map.
Bohnanza (The Bean Trading Game)
A card game almost entirely built around negotiation. You plant and sell different types of beans, and just like in Catan, the key is trading well with other players to come out ahead.
Small World
Here you control civilizations expanding across a shared map and competing for territory, with the twist that each civilization has an expiration date and needs reinventing mid-game. The territory control and constant interaction feel a lot like Catan.
Alhambra
You buy tiles to build your own city using different currencies, balancing planning with what shows up in the shared market. If you like Catan's building side more than its dice-rolling, this is a solid pick.
Puerto Rico
Resource management, production, and maritime trade between colonies, with more strategic depth than Catan and less reliance on luck. Great if you want longer, more calculated games.
Terraforming Mars
Swap the island for the red planet: you generate resources, build infrastructure, and compete to turn Mars into a habitable place. It's denser than Catan, but shares that same feeling of building your production engine turn by turn.
Where to play them for free
Most of these titles are available on platforms like Board Game Arena, where you can play from the browser with a free account (with some usage limits that lift with the premium version).
If what you're after is the Catan-style genre itself without the limits of the official versions, give Hexo a try, an independent hexagonal strategy game inspired by this kind of settlement game: head to /play/ai and play free against the AI whenever you want.
