Sugiyama has layers and can be used for trees just as well (and may give nicer results for almost-trees than removing non-tree edges and routing them individual

Sugiyama has layers and can be used for trees just as well (and may give nicer results for almost-trees than removing non-tree edges and routing them individually). KIELER and ELK seem to be collections of various layout algorithms, including Sugiyama and specialized tree layout algorithms (same with our own library yFiles).