In the spare half-hours between real work and eat and sleep I reimplemented TeX's layout algorithm, on the minimal motivation of at least proving to myself that, after all's said and done, it isn't really that complicated. And it isn't! Here is a PDF. Text is from the twelf page, font is mine but largely derivative of tom7's, algorithms by Knuth et al. Hyphenation is not automatic yet, (i.e. I put in all optional hyphenation points by hand, but the algorithm automatically chooses which ones to use) but that should be easy.

Oh, also I haven't got the thing that discourages two consecutive hyphenated lines, which you can probably tell from the two consecutive hyphenations in the example. That's pretty easy to add back in.