xBR
A rule-based pixel-art scaler that works out which way an edge runs and rounds it off without smearing the rest of the image.
The name is short for "scale by rules", and its author is known only by the handle Hyllian. Released in 2011, it looks at a wider window than hqx: for each corner of a pixel it weighs colour distances along two diagonals against each other, and whichever direction looks more like an edge wins. Colours are then blended along that edge only.
The result keeps curves and thin lines intact better than its predecessors, and the filter exists both as CPU code and as a shader. Zenju's xBRZ variant is used for texture scaling in emulators, and Super-xBR from 2015 reworks the whole thing into two passes so it can handle arbitrary scale factors.