MathFlow for XMetaL 1.9 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus. The most popular version among MathFlow for XMetaL users is 1.9. The program belongs to Education Tools. This program was originally developed by Design Science, Inc.
From the developer:
MathFlow Editor is a native MathML equation editor that works with XMetaL Author and XMAX. MathFlow Editor's user experience is similar to how Design Science's MathType and Equation Editor products work with Microsoft Word — the operator double-clicks on an equation in an XML document and it automatically opens in the MathFlow Editor window.
You may want to check out more software, such as XMetaL Author Enterprise or MathFlow SDK, which might be related to MathFlow for XMetaL.