RefDB is a reference database and bibliography tool for SGML, XML, and LaTeX documents, sort of a Reference Manager or BibTeX for markup languages. It is portable and known to run on Linux, Free/NetBSD, OSX, Solaris, and Windows/Cygwin.
Apostilator is a XML based front end to LaTeX that simplifies the process of writing all kinds of documents from letters to books, reports and articles. It's easy to customize and create templates defining a style for all your documents.
Latexss is a program that can transform a text file with a very minimal style syntax into a self contained LaTeX spreadsheet powered by the fp package. A graphical front-end (klatexss) is provided to generate both the text and the LaTeX file.