Mozilla Thunderbird is the e-mail client I install on all my PCs as a free alternative to Microsoft Outlook. It’s worked great for me until I began working in an environment where the use of vCalendars is common. After installing the ‘Lightning’ add-on, I no longer see the raw vCalendar data but the nicely formatted invitation to a meeting.
Installing the add-on is easy. Simply launch Thunderbird and navigate to Tools > Add-ons.