500px is a Flickr alternative with a commercial bent, encouraging you to sell your best photos and buy other people's(!) And now we have a full UWP app for the service, dubbed Perfect 500px - yes, from the developer behind the likes of Perfect Tube. It's fairly fully featured, with just a few rough edges at the moment, so make sure to give some feedback and get involved.

From the Store description:

The best third-party 500px app designed exclusively for Windows 10 Universal. Stay inspired with a continuous feed of the world’s most incredible images, connect with 7 million photographers, and share your best work with a passionate community.

• Share your photos with the world and get recognized by international brands
• Collect photos based on your personal visual style with Galleries
• A unique discovery experience ensures everyone has a chance to get noticed, and keeps you up to date on the latest and greatest from the 500px community
• A sleek home feed will keep you scrolling through inspiring images from the people you follow, and recommendations based on the photos they like
• All photos are displayed uncropped and at the highest quality - your photos have never looked better on a mobile device!
• Automatically updates lock screen/desktop/mobile start screen wallpaper from any Gallery or Photo

A few screenshots of Perfect 500px in action on my Lumia 950 XL:

The quality level of 500px is high, as you'd expect, considering that most uploaders are intending, at some point, to sell their images... (right) searching works brilliantly, with related tags as well.

The hamburger menu for Perfect 500px - and yes, there's a light theme if you really want it(!); (right) starting to upload some of my own best images - though one glitch is that you can't change their titles or descriptions. Yet.

And the obligatory Continuum shot, proving the UWP app's chops:

Another useful UWP starting point for online services from this developer. You can grab this for free in the Store here.