Live demo: https://chearon.github.io/dropflow/

It matches browsers in all cases I can find where they agree, and it's fast. It supports `position`, `inline-block`, `z-index`, and complex properties like `float` and `vertical-align`. It doesn't support high-level layout like flexbox or grid yet, but you can get intrinsics to easily divide space yourself and paint multiple layout trees. It has a great text layout implementation, and supporting non-Latin scripts is a top priority.

I've wanted this to exist as far back as 2013, and the desire kept coming up: for a way to get detailed intrinsics, for high quality rich text layout to canvas and SVG, and for server-side rich text. We currently use it in CellEngine for our new canvas-based spreadsheet library to layout text in hundreds of thousands of cells, and will be using it soon to render PDFs with thousands of pages in a few seconds.