As a .NET developer it's nice to see projects like these. On the other hand I had looked at this a while back and my impression of the data model (specifically the Product class) was not great.

https://github.com/simplcommerce/SimplCommerce/blob/master/s...

Price, OldPrice, SpecialPrice, special price start and end dates properties are less than ideal for any non-trivial implementation. Prices should be driven by policies, not defined in the product itself (IMO.)