Photile is a small JS/GO app that I've built to learn ReactJS and Golang.
It can be used to create a perfect cover image for your Facebook, Twitter or any other social profile. You can use it to create featured images for your blog articles or even print it out and put it on your wall.
It can also be used to create "end of year" or "best of Instagram" collages.
Neat! I'm not sure the HN crowd is your target audience though.
I encourage you to showcase your app on Reddit (/r/reactjs, /r/sideproject) and ProductHunt.
Thank you for your suggestions. I did plan to showcase it on ProductHunt and this was just a first stop :-) I did not consider those subreddits so I'll give them a try.