There's apparently an executable version of waifu2x with a few more scaling options which is more convenient than using the online version:
https://github.com/lltcggie/waifu2x-caffe/releases
Topaz gigapixel is similar too, but it uses a different method to upscale images and is usually better for realistic photo stuff…
Hey, so I discovered this cool japanese site, Waifu2X which is intended to upscale anime images but it works great on anything else. It uses a neural network and the technology is really promising Im working on some showcase stuff but all my weapon sprites are only 425x115 and re-rendering them all would be a huge effort,…
I used ON1 for up-rezing some textures. It also worked well for what it does. Maybe not the right thing for linework or non-noisy art but worth checking out. https://www.on1.com/products/resize/