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A Calendar User Agent (CUA) is software that supports the iCalendar specification. This page provides information regarding the different categories of CUAs.

Rich Clients

Microsoft Outlook

Language: C (?)
License: Proprietary

RFC2445 Deviations: * allows DATE-TIME representation without specifying a VALUE=DATE-TIME parameter * Outlook will not read files that don't contain the mandatory UID and DTSTAMP properties in VEVENT, etc. components * provides quoted TZID parameters, and as such does not conform with RFC2445 * generates additional spaces in recurrence rules containing a BYDAY component * 2003 will only accept folded lines of exactly 75 octets * 2007 will fold lines with all folded lines starting with a tab instead of spaces
Non-standard Properties: * X-MICROSOFT-CDO-BUSYSTATUS:TENTATIVE * X-MICROSOFT-CDO-IMPORTANCE:1 * X-MICROSOFT-CDO-INTENDEDSTATUS:BUSY * X-MICROSOFT-DISALLOW-COUNTER:FALSE * X-MS-OLK-ALLOWEXTERNCHECK:TRUE * X-MS-OLK-AUTOSTARTCHECK:FALSE * X-MS-OLK-CONFTYPE:0 * X-MS-OLK-SENDER;CN=Test:mailto:user@example.com

Lotus Notes

Language: C (?)
License: Proprietary

RFC2445 Deviations: * Requires METHOD:REQUEST for non-optional attendees
Non-standard Properties: * X-LOTUS-BROADCAST:FALSE (required for non-optional organizer?) * X-LOTUS-CHARSET:UTF-8 * X-LOTUS-UPDATE-SEQ:1 * X-LOTUS-UPDATE-WISL:$S:1;$L:1;$B:1;$R:1;$E:1;$W:1;$O:1;$M:1 * X-LOTUS-NOTESVERSION:2 * X-LOTUS-NOTICETYPE:I * X-LOTUS-APPTTYPE:3 * X-LOTUS-CHILD_UID:9DA9112BB4438073C125750E004B7055

Mozilla Calendar

Language: C (?)
License: MPL

RFC2445 Deviations: * long content lines are folded with a single LF character (should be CRLF) * folds all property parameters and values * Generates non-standard "X" properties

Apple iCal

Language: Unknown
License: Proprietary

RFC2445 Deviations: * uses VALUE=TEXT on some X-properties (NOTE: this is valid behaviour) * iCal events don't include the mandatory DTSTAMP property * iCal 1.0 doesn't appear to include VTIMEZONE definitions where applicable (this appears fixed as of 1.5)

Evolution

Language: C (?)
License: GPL

KOrganizer

Language: C (?)
License: GPL

RFC2445 Deviations: * long content lines are folded with a single LF character (should be CRLF) * folds all property parameters and values

Chandler

Language: Python
License: GPL


k5n Desktop Calendar (k5nCal)

Language: Java 1.5
License: GPL (3rd party libraries with other licenses)

Web Applications

PHP iCalendar

Language: PHP
License: GPL

RFC2445 Deviations: * long content lines are folded with a single LF character (should be CRLF)

Webical

Language: Java
License: GPL

Google Calendar

Language: Unknown
License: N/A

RFC2445 Deviations: * Generates DTSTART properties in DATE format without specifying the required VALUE=DATE parameter

WebCalendar

Language: PHP
License: GPL

RFC2445 Deviations: * Generates invalid ATTENDEE lines

Calendar Servers

Hula Project

Language: Unknown
License: GPL

Cosmo

Language: Java
License: Apache 2.0

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