This is a Nikoli original. It was originally Nuruomino, but the name was changed to refer to the nicknames for the four types of tetrominoes allowed by the rules.
Puzzle and Goal
An unsolved puzzle consists of a rectangular grid with regions drawn out.
The goal is to color in an orthogonally contiguous area.
The solved grid must satisfy the following conditions:
Each region contains exactly one tetromino. A tetromino is an orthogonally contiguous area of four cells.
No 2x2 area can be completely colored in.
No two tetrominoes of the same shape can be orthogonally adjacent.