Basic Web Stuff
XML
XHTML - eXtensible Hypertext Markup Language
XML Schema
XML Namespaces
XSL
XML Base
XML Infoset
XLink
XInclude
XPath
XQuery
XForms
XML Signature
XML Encryption
XML Key Management
URI - Uniform Resource Identifier

Digital Identity / Identity Federation
OpenID
SAML - Security Assertion Markup Language
WS-Federation
XACML - eXtensible Access Control Markup Language
Liberty ID-FF
Liberty ID-WSF
OAuth
SPML - Service Provisioning Markup Language

Social Graph / Social Networking Related
SIOC - Semantically Interlinked Online Communities
FOAF - Friend Of A Friend
XOXO
XFN - XHTML Friends Network
iCal
vCard
XUP - XML User Profiles

Web Services
UDDI
SOAP
WSDL
WS-Policy
WS-Addressing
WS-Security
WS-SecurityPolicy
WS-Trust
WSRF - Web Services Resource Framework
WSRP - Web Services for Remote Portlets
WS-Eventing
WS-MetaData Exchange
WS-Inspection
WS-Discovery
WS-ReliableMessaging
WS-Transaction
WS-Notification
WS-Transfer
WS-Topics
WS-SecureConversation
List of Web Services Specifications

Semantic Web
RDF - Resource Description Framework
RDF Schema
OWL - Web Ontology Language
OWL-S
Dublin Core
ODM - Ontology Definition Metamodel
SPARQL - SPARQL Protocol and RDF Query Language
RQL - RDF Query Language
RDFa
SRU - Search/Retrieval via URL
SKOS - Simple Knowledge Organisation System
SIOC - Semantically Interlinked Online Communities
RDDL - Resource Directory Description Language
POWDER - Protocol for Web Description Resources
GRDDL - Gleaning Resource Descriptions from Dialects of Languages
SWRL - Semantic Web Rule Language
SWSF - Semantic Web Services Framework
RIF - Rule Interchange Format
KIF - Knowledge Interchange Format
OKBC - Open Knowledge Base Connectivity
WSML - Web Services Modeling Language
WSMO - Web Service Modeling Ontology<
F-Logic
SUO - Standard Upper Ontology

Blogging / Syndication
RSS - Really Simple Syndication
Atom
Atom-OWL
Atom Publishing Protocol
Atom Threading Extension
APML - Attention Profiling Markup Language
OPML - Outline Processor Markup Language
XBEL - XML Bookmark Exchange Language
MetaWeblogAPI

Microformats
GEO
hCalendar

Management
WSDM - Web Services Distributed Management
WBEM - Web Based Enterprise Management
SNMP - Simple Network Management Protocol
CBE - Common Base Event

Document Formats
CDF - Compound Document Format
ODF - Open Document Format
Docbook

Directory Services
LDAP - Lightweight Directory Access Protocol
DSML - Directory Services Markup Language
LDIF

Metadata

CWM - Common Warehouse Metamodel
MOF - Meta-Object Facility
MOF QVT
CIM - Common Information Model
XMI - XML Metadata Interchange

Uncategorized
OpenSearch
OpenGIS
SyncML
XBRL - Extensible Business Reporting Language -
XTM - XML Topic Maps
FIPA - Foundation for Intelligent Physical Agents
AIML - Artificial Intelligence Markup Language
XMPP - Extensible Messaging and Presence Protocol
DIAL - Device Independent Authoring Language
SMIL - Synchronized Multimedia Integration Language
XFML - eXchangeable Faceted Metadata Language
Groves
XRI - eXtensible Resource Identifier
XDI - XRI Data Interchange
I-names
MDA - Model Driven Architecture
OCL - Object Constraint Language
UML - Unified Modeling Language
BEEP - Blocks Extensible Exchange Protocol
XUL