Six Apart font here refers to the font used in the logo of Six Apart, which is a software company known for creating software like the Movable Type, TypePad and Vox.
The font used for the Six Apart logo is probably Alternate Gothic designed by Morris Fuller Benton, who designed them as complementary weights of his other sans serif types, namely, Franklin Gothic and News Gothic. More details about it can be found here.
Download Alternate Gothic Font
The Alternate Gothic font identified above is not available for free, please follow the link above and purchase the font. Meanwhile, you can take a look at our collection of fonts for cars, pop music and apparel as well as round-ups of new & fresh fonts around the web.