.xml - XML document
.000 - Linux, FreeBSD file
.ctt - Windows Live Messenger Contact List
.metadata_never_index - MAC OS X metadata settings file
.pst - Microsoft Office Outlook personal folder file
.part - Mozilla Firefox partial download file
.uccapilog - Windows Live Messenger file
.mso - Microsoft Orgchart file
file extension ERF - SGML Visual DTD entity reference file
File extension ERF description:
SGML was originally designed to enable the sharing of machine-readable documents in large projects in government, law and industry, which have to remain readable for several decades—a very long time in information technology. It has also been used extensively in the printing and publishing industries, but its complexity has prevented its widespread application for small-scale general-purpose use.
Primarily intended for text and database publishing, one of its first major applications was the second edition of the Oxford English Dictionary (OED), which was and is wholly marked up using an SGML-like markup.