AddEvent - AddEvent is an Add to Calendar button for one-time and multiple events.
Cal.et - Add to Calendar Link Generator
Microsoft Outlook Calendar - Calendar is a time-management web application by Microsoft.
Calndr.link - Dead simple & free add to calendar links + API
Button for Google Calendar™ - See your daily schedule and join meetings in one-click.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.