Minefield, HTML5 Massively Multiplayer Online Minesweeper

I wonder if it's possible to create a minesweeper layout that can't be solved without guessing at least once or not.

All layouts technically fit that description, since you have to guess once for your first move.

Beyond that, though, a hollow 3x3 ring of mines also requires guessing, since there's no way to tell whether the center square is a mine or not. There's lots of other such situations as well.

Depends on the implementation - some (e.g. Windows') don't fit there as it is dynamically generated after the first click so the player never loses on the first move other than in "retry this layout" modes.

Interesting point with the 3x3 ring.

This is a good concept, and executed well. What is the backend and is this open source?

The title of this post got my upvote!