This one will be very familiar to a lot of you. I guess this is the format that is most commonly used for date/timestamp representation. But despite that, many people don't know that this standard also defines a format for durations and time intervals.
The OAuth spec is an authorization framework that describes how a third-party app can access resources own behalf of a user. It has various flows depending on the trustworthiness or the use case of the developed client. OAuth is used by many well known names that also function as authorization provider.
Describes a format based on JSON that is used to interchange geospatial data.
Often seen as iCal or
.ics files, iCalendar is a specification to exchange calendar and scheduling information. There is a variety of use cases where this format is used (calendar events, to-dos, journal entries, and free/busy information for e.g. meeting rooms). So if you accept a meeting invitation and put it into your calendar app, there is a good chance it was sent in iCalendar format.
(jCal is the JSON representation)
These rfc describes a format for exchanging a variety of information about individuals (name, phone number, email, etc...). If you want to share a contact from your smartphone, often vCard is used to share that infos.
(jCard is again the JSON representation)
What standards/rfcs am I missing that you use in your daily work? Let me know