Currently, this is the best digital adaptation of Settlers of Catan that I know of. The interface is user-friendly, straightforward and very smooth, it almost makes me prefer this than the real tabletop game. Other than microtransactions, its main downside is on the technical side; matchmaking and scoring systems often feel clunky, and there are a couple of annoying achievement-related bugs.

its catan, you either love it or hate but it does a good job of adapting the board game
the main game is free and you can play it anytime, but you need to pay if you want any of the expansions

Just use colonist.io.

Ranked: All Time

I love Catan but wish this version would allow you to play with more than one map.