TheSudoku.com
Sudoku Rules
Easy
Normal
Hard
Expert
Master
Chains & Colours
3D Medusa
Advanced multi-digit coloring across interconnected candidates
Dual Medusa
Two-coloring using a single digit
Forcing Chains
Following logical consequences from an assumed candidate
Nishio
Trial a candidate and eliminate it if it leads to a contradiction
Dynamic Forcing Chains
Forcing chains that branch through multiple logical possibilities