Real-ESRGAN is described as 'aims at developing Practical Algorithms for General Image/Video Restoration' and is a Image Upscaling App in the category. There are more than 10 alternatives to Real-ESRGAN for a variety of platforms, including Windows, Online / Web-based, Android, Mac and Linux. The best alternative is waifu2x, which is both free and Open Source. Other great apps like Real-ESRGAN are Gigapixel AI (Paid), Waifu2x Caffe (Free, Open Source), Bigjpg (Free) and AI Image Enlarger (Freemium).
Gigapixel AI helps you do a single thing very well: increase image resolution in a natural way. This is pretty hard to do. Most upscaling algorithms don’t know how to accurately fill in missing pixels, so you end up with blocky low-quality results.
Waifu2x Caffe rewrites only the conversion function of the image conversion software "waifu2x" using Caffe and is software developed for Windows. Although it can convert with CPU, using CUDA (or cuDNN) can convert faster than CPU.