XOXO (eXtensible Open XHTML Outlines) is an XML microformat for outlines built on top of XHTML. Developed by several authors as an attempt to reuse XHTML building blocks instead of inventing unnecessary new XML elements/attributes, XOXO is based on existing conventions for publishing outlines, lists, and blogrolls on the Web. The XOXO specification defines an outline as a hierarchical, ordered list of arbitrary elements. The specification is fairly open which makes it suitable for many types of list data. E.g. the more semantic version of the S5 presentation file format is based upon XOXO.
XBEL, or the XML Bookmark Exchange Language, is an open XML standard for sharing Internet URIs, also known as bookmarks (or favorites in Internet Explorer). An example of XBEL use is the XBELicious application, which stores Del.icio.us bookmarks in XBEL format. The Galeon, Konqueror, Arora and Midori web browsers use XBEL as the format for storing user bookmarks. XBEL was created by the Python XML Special Interest Group [1] "to create an interesting , fun project which was both useful and would demonstrate the Python XML processing software which was being developed at the time," [2].
Leo is... * A general data management environment. Leo shows user-created relationships among any kind of data: computer programs, web sites, etc. Leo shows multiple views of data within a single outline. * An outlining editor for programmers. Leo supports optional noweb and CWEB markup. * A flexible browser for projects, programs, classes or any other data. * A project manager. * Fully scriptable using Python. * Leo's outline files are XML format.
PXSL – Parsimonious XML Shorthand Language PXSL ("pixel") is a convenient shorthand for writing markup-heavy XML documents. It provides XML authors and programmers with a simple, concise syntax that they can use to create XML documents. For more advanced users, PXSL offers customizable shortcuts and sophisticated refactoring tools like functional macros that can markedly reduce the size and complexity of markup-dense XML documents. The short version is this: PXSL is XML turned inside-out. Instead of tagging the structure, you tag the non-structure, which is the better approach when most of your information is structure.