Implementing Virto Calendar for SharePoint Online was a no brainer for my team. After a free trial, we quickly saw what an amazing solution it is. We have been able to extend SharePoint's out of the box calendars with this app to create beautiful, interactive calendars. We even developed a conference room booking system for one of the premier sporting facilities in the US. based on the features available with Virto Calendar. The Virto team is also very quick to add new features to the application. I have seen it evolve over the past 2 years into an app we just can't live without. It seems they listen to their customers and implement the features that are needed most and lacking in the default SharePoint calendaring experience. I could not recommend a better app for SharePoint online calendaring.