FXAA
Anti-aliasing that runs as a post-process pass on the finished frame — it hunts for edges in the brightness and blurs them, cheap but a little mushy.
Timothy Lottes at Nvidia presented FXAA (fast approximate anti-aliasing) around 2011. Unlike MSAA it ignores geometry entirely: it works on the already-rendered image, finds edges wherever luminance jumps, and smooths them in a single shader pass.
Because it only sees finished pixels, it works just as well in deferred rendering and on HDR images, costs almost nothing, and is trivial to bolt on. The downside is that the whole image softens slightly, text and fine detail lose crispness, and sub-pixel information that was never there cannot be recovered. It spawned a whole family — MLAA, SMAA — that refine the same idea.