You were once one cell. Every part of you, skin and bone and blood and brain, is a great-great-grandchild of it. Start as that one cell and choose, split by split, what it will become.
Six rooms: Grow (the cell tree), Split (one cell into a whole body in 45 doublings), Zoom (a microscope, true to scale), Inside (the parts of a cell and the book they all share), Rescue (send the right cell) and Album (every cell you have grown). English, 日本語, 中文. Part of Zoey's Lab.