GroupDAV is a computer protocol used to connect Open Source groupware clients with Open Source groupware servers. Its primary design goal is to be as simple as possible to implement, focusing more on end-user issues with open source applications than on an extremely extensive command set. It is based on a subset of WebDAV.
Client side GroupDAV implementations exist for KDE Kontact, Evolution, Thunderbird and Outlook, work on the Mozilla Calendar Project is in progress. Servers include OpenGroupware.org, SOGo, the Citadel system and eGroupWare. In addition WebDAV + CalDAV + CardDAV server is implicitly a GroupDAV v2 server.
GroupDAV's relationship to CalDAV is viewed differently by different developers. Some of the earliest implementors intended it as a protocol complementary to the CalDAV effort, because CalDAV provides more extensive operations on calendar folders. Others have positioned GroupDAV as the leading protocol, citing CalDAV's excessive complexity as a source of interoperability bugs. This dichotomy is likely to become irrelevant in the future, however, as it is straightforward for a server to simultaneously support all variants.
GroupDAV is now considered by some to be a subset of CalDAV (RFC 4791) and CardDAV (RFC 6352) intended for less complex applications.