- BioLit (Lynn Fink, Phil Bourne, OBO, Science Commons) (project homepage)
- Chem4Word (Jim Downing, Peter Murray-Rust)
- NLM DTD Article Authoring (Pablo Fernicola)
I think Tony Hey is probably involved with most of these.
See also Lemon8-XML (MJ Suhonos, PKP). Not actually a Word Add-in, but useful for converting existing Word/ODT documents into the NLM DTD.