| API | Description | Category | |
|---|---|---|---|
| 30 Boxes | Calendar service | Calendar | 2006-02-24 |
| Eventful | Events discovery and demand | Events | 2005-10-31 |
| Google Calendar | Calendar service | Calendar | 2006-04-20 |
| Holidays Service | Holiday dates lookup service | Reference | 2006-10-20 |
| Notely | Academic notes and calendar service | Utility | 2007-12-30 |
| Orange Personal Calendar | Calendar service | Calendar | 2008-03-16 |
| Upcoming.org | Collaborative event calendar | Events | 2005-11-19 |