When I first learned about Calendly I was sceptical a bit, as I did not know what to expect. Also, I doubted I need another application for a calendar. I had Outlook, didn't I? Well it turns out, that when you need to arrange meetings with people external to your company, it can be a bit tedious processes, especially, when doing so over email.
Once I had a need indeed to arrange for a meeting but did not want to play the email ping-pong to find the right time. I then created a free Calendly account. You know what? I loved it. It's really easy to register and set up. Arranging a meeting is really simple with this tool. You just set up your availability in a clever way, even when you work in shift patterns you can set different availability on different days.
So how does it work? You tell the app what time you are available on what days, you link your calendar and predefine time slots, e.g. 15, 30, 60 minute slots. You share your Calendly link to the party you want to meet with and they can book a slot in your calendar, of course considering events that are already there. Your events are not visible, only time slots are visible. Very simple, yet extremely effective. You don't have to exchange emails to find the right time to meet.
There aren't many downsides, the main downside for me is that the free account allows you to only predefine one time slot, e.g. 30 minute. This means, that when somebody wants to meet with you, they will only have a chance to save a 30 minute window in your calendar. If you want more options, you have to pay 8 bucks a month or 12 for the pro version. There are many extra options, but if you want something extra, you have to pay extra. Free of charge version is very good, especially when you meet externally only occasionally. For me the free version is just fine. I definitely recommend Calendly to anyone who meets with clients and other external parties. You can always get the free version and decide later whether or not to upgrade.