Photopea allows dragging & dropping images in to the browser window to upload them and add to the scene.

As it is an HTML5 application, running it requires no additional plugins on modern browsers.

This means you can open these files in Photoshop, so if you don't have Photoshop on one device, you can still export your Photopea project and continue editing on Photoshop on another device

Works on all standard browsers, without additional plugins (does NOT require Flash, for example).