For some time now I have been aware of the Family Search project called "Community Trees," but I have to admit that I did not really understand what it was all about.
Community Trees are lineage-linked genealogies from specific time periods and geographic localities around the world. That is the stock explanation of the project. It gets a bit clearer if you read a recent article by Dick Eastman in his Online Newsletter. Dick combines the project description from Family Search with his own insights.
This collection, like all of the Family Search offerings is free. You might find it beneficial to your research, but I recommend you read Dick's article first. You can find it at http://goo.gl/qqZpQ