Great question! Yes, there are downpayment assistance programs from the City of Modesto and Riverbank. Since your question linked to Home Buying in Modesto, that information is here:
This link shows two programs, the first is for homes that have been acquired and rehabilitated through the Neighborhood Stabilization Program. The second, is more general, to allow for a broader selection of homes.
I hope this helps, and let me know if I can answer any more of your questions or help you through the process.