Q: Is GroupDAV a replacement protocol for CalDAV?

No! GroupDAV has a different focus, which is to connect OpenSource and free groupware servers with OpenSource and free groupware clients. This keeps the GroupDAV requirements much simpler than what is required for CalDAV.
It is a major goal of GroupDAV to make it easy for servers to support both GroupDAV and CalDAV (for example a server might choose to use CalDAV for scheduling and GroupDAV for contacts).

Q: Why did you create GroupDAV?

The GroupDAV draft is the result of the Kontact/OGo hack-o-ton which took place in October 2004. The participants agreed that the protocol OGo used to connect Kontact should be very useful for various clients and servers. That proved to be right.

Q: Is GroupDAV an OpenGroupware.org / Kontact only effort?

No. The initial implementation was done to connect the KDE Kontact client to the OpenGroupware.org ZideStore server but we quickly discovered that the same approach would be viable for other servers and clients.
Soon after the draft was released an Evolution GroupDAV adaptor was created as part of the Noodle project. In early 2005 the Citadel server added support for GroupDAV.
We try to maintain a: list of implementations.

Q: Can GroupDAV be used to integrate groupware data into other web-apps?

Currently not. The current draft requires that the client keeps an offline cache of the server data. Indeed GroupDAV basically specifies how such a cache is to be kept in sync with a server.
Online access is something which should be well covered by the CalDAV protocol and is currently considered out of scope for GroupDAV.

Q:Why is GroupDAV such a good match for OpenSource clients?

All the major OpenSource clients - Kontact, Evolution and Sunbird - store their content in the iCalendar and vCard formats and are built around the data model of those.
Further GroupDAV is based on HTTP which is widely supported, all of the mentioned clients have full fledged HTTP client libraries built in. Notably GroupDAV only reuses a few constructs of WebDAV to keep the protocol very easy.

Q: Does GroupDAV cover mail functionality?

No. While the IMAP4 protocol is quite complicated and hard to implement properly and completely, its well established. All relevant mail clients have proper support for IMAP4.
However GroupDAV resources may refer to IMAP4 URLs to access mail folders which are part of the GroupDAV server hierarchy. The exact way to accomplish that is currently open for discussion.