-Make your headline a different color other than white, because it's very hard to see with that background image.
-It took me scrolling "below the fold" to find out what it is this product does. I'd change your headline to something more concrete, like "Gmail, the way you want it" while also finding a way to move up some of the product-specific content higher up on the page.
-You also have way too much text and the two paragraphs that start with "Gmelius, pronounced 'Gmail'-'jus'..." seem unnecessarily long and distract me from finding out more about your project. I actually read that and just skipped past that whole block of text and later realized I had also overlooked your donation box.
-There's also too much text explaining the features, making those screenshots look tiny in comparison. I think you could just get rid of the descriptive text and keep the feature titles, like "Restore the old compose window" and "Experience Gmail without ads" without losing any of the message.
-Minor point: That red download box should explicitly tell me it's not supported for Safari, if you're detecting my browser. Right now it says "Free Download for Safari" in bold text with "Browser not supported" in a lighter typeface underneath. Like I said, minor, but I found it a bit confusing.
Hope that helps!