Using Cal on a daily basis. Its customizability is a god send.
Their rate of product development is astounding and the reason why I believe they are already the best product in the market.
Disclaimer: Fan and investor 😊
It's pretty easy to setup and offers a ton of nice features. I embed it on my website and have link to my profile in my email footer. Works very well, can't wait to use it even more in the upcoming months.
Had an issue logging in and Peer (CEO) tended to the matter within the hour. I haven't had such responsive customer service so this was quite the experience. It's refreshing to find a customer-centric open source project do so well.