Mozilla Calendar

Buni Meldware Communication Suite   (Compare Project)

License: lgpl

DAViCal CalDAV & CardDAV Server   (Compare Project)

Mostly written in PHP

License: gpl3

mozPod   (Compare Project)

Mostly written in PHP

License: gpl, lgpl, mozilla_public_1_1

OBM   (Compare Project)

License: AGPL3_or_later

WebCalendar   (Compare Project)

Mostly written in PHP

License: academic

Bedework Enterprise Calendar   (Compare Project)

Mostly written in XSL Transformation

License: apache_2

citadel   (Compare Project)

Mostly written in C

License: gpl3

Java Calendar Tools   (Compare Project)

Mostly written in Java

License: gpl

Evolution   (Compare Project)

Mostly written in C

License: lgpl21_or_later

DavMail POP/IMAP/SMTP/Caldav to Exchange   (Compare Project)

Mostly written in Java

License: GNU-GPLv2