It is available as an OpenGL extension from at least one vendor. In this technique additional subpixel storage is maintained as part of the color, depth and stencil buffers. Instead of using alpha for coverage, coverage masks are computed to help maintain sub-pixel coverage information for all pixels.
Current implementations support four, eight, and sixteen samples per pixel.
This technique does not entirely replace the methods described above, but is complementary. Antialiased lines and points using alpha coverage can be mixed with multisampling as well as the accumulation buffer antialiasing method.