PPG is selling something called Aquapel:
"Using technology innovated for the aviation industry, PPG's Aquapel® Glass Treatment forms a chemical bond with the glass which increases water repellency, causing it to bead and easily shed off the glass. These fluorinated compounds apply in just minutes to a clean, dry windshield or any exterior glass surface, and last up to six times longer than silicon-based products.
Additionally, Aquapel® Glass Treatment remains highly effective after months of normal use, including driving in rain and snow, car washing, and glass cleaning."
You can buy it on eBay. I have not tried it, but probably will as PPG clearly (no pun intended) knows a thing or two about glass. Have used Rain-X and find, like most do, that it workd, but quickly (couple of weeks at best) wears off.