Calcium provides interactive calendars you can use through your browser. Features include: dynamic calendar merging (events from one calendar can be included in another), multiple views and formats, repeating events, email support, extensive color and font customization, support for full HTML in the event text and calendar headers and footers, popup text associated with any event, searching and filtering, multi-language support, a flexible security model, and more. Calcium is very easy to use, and fully supported by an established company. It runs anywhere that supports Perl CGIs; no non-standard Perl modules are necessary. Full 2-way synchronization with Palm Pilots or MS Outlook is available; iCalendar "subscriptions" are supported too.
Calendars for the Web provides a server based calendar and scheduling application. It allows unlimited users to share unlimted events per calendar. Calendars for the Web comes with a full-featured browser based interface, is completely customizable (sixteen different calendar view types), fully documented, and supports online administration.
E*Reminders is a series of PHP scripts that interact with a MySQL database to setup email reminders for any events or occasions you'd like. It includes recurring reminders, advance notices, and password authentication for email addresses. It can be used for an entire company, as a service for Internet users on your site, or privately.
LowCal is a lightweight Web-based calendar of events. It is designed to allow you to announce events that have already been planned (it's not "groupware" and doesn't do "calendaring") without requiring the installation of PHP or a database backend. Events can be categorized and users can choose to display one, multiple, or all categories. Viewing modes include tabular monthly calendars and plain event lists, with or without details. Recurring events are well-supported using a cron-like syntax. All display is template-based, allowing complete configurability.
Project-Based Calendaring System (PBCS) is an open source Web-based calendaring system, designed to be a useful tool for project managers or project planners. It allows users to have appointments of multiple people in one overview, making it easy to plan appointments for projects in the future. There are special overviews to see all appointments at once for a week or a month. There is also a section to add notes or reminders.
TUTOS (The Ultimate Team Organization Software) is a groupware, ERP (Enterprise Resource Planing), CRM (Customer Relationship Management), and PLM (Project Lifecycle Management) suite that helps small to medium teams manage various things in one place. Its features include personal and group calendars, an address book, product and project management, bug tracking, installation management, test management, scrum management, a task list, notes, files, mailboxes, and useful links between all of the above.
Vanilla is a WikiClone written in REBOL. It is useful for collaboratively working on projects, tracking todo items, managing adresses, and creating Web logs. All page editing takes place in the browser. Vanilla features a simple templating system, a full-featured user and session management system, and an extension architecture for writing simple Web applications in REBOL.
WebCal is a free browser-based calendar program to help you keep track of your appointments, meetings, birthdays, etc. It's simple, yet has powerful scheduling features, email reminders, and a user-friendly interface, and being Web-based makes it ideal for use by groups of people.
NullLogic Groupware is a modular Web-based groupware and email system designed for contact management and event scheduling. Additional features include private messaging, public discussion forums, webmail, shared bookmarks, file sharing, call tracking, order processing, an XML-RPC API, and integrated POP3 and SMTP servers.