The S9 has the same chassis as the S10, but it comes with a smaller, 9 inch screen instead of the 10 inch screen that you get on an S10. (I wonder how they came up with these names?) That means you get the same touch-typable keyboard on both models, but the S9 has an unattractive bezel around the edge of the screen. But it also has the low starting price of about $340 US.
The cheapest S9 models will likely run Linux and have 512MB of RAM and 80GB hard drives. There’s no word on whether the S9 will actually ship anytime soon or if it will be plagued by the same delays affecting S10 shipments in the US. Last I heard, Lenovo has no plans to make the S9 available in the US at all.