Hey there, I'm glad you know about GDevelop (http://compilgames.net/) as it is a fantastic piece of software and a worthy rival to Construct 2. Florian is a genius and I'm really excited to see where he takes GDevelop next.
Unfortunately, as amazing as Florian is, he did not create the assets used in the platformer template included in GDevelop. Those assets were created by Kenney and can be seen on his website (http://kenney.nl/) or alternatively, here on itch where he sells them as bundles - https://kenney.itch.io/.
I highly recommend Kenney's assets if you are (like me) a terrible artist! Even if you are pretty talented at art (or have someone on your team who is) they can still be brilliant for rapidly creating prototypes.
If you take another look at the description for my Platformer Template you'll see that I credit Kenney for creating the assets.
Thanks for your feedback!