I've been struggling a lot with SEO whilst building my startup, and I happened upon a pretty great collection of sites on the internet where you can submit your startup. It takes a while to go through all, but it's great for backlink juice and just general traffic (people use them to discover new products, like e.g. alternative.to).
Here's the GitHub repo with the huge collection of places: GitHub
Not all of them are good tough: like a third of them aren't free and can cost up to ~199$ just to list your project. I went through all of them yesterday posting Namy (my startup), and made my own collection of the best/fastest. Then, since I need SEO juice for Namy, I published them in a blogpost:
Hope you find this useful for your own projects!!