Take the basic entrance door - a solid core door that was the first to come in a 3' or 36" width. They have come in plain front (called "flush"), raised panel (one to as many as ten), carved for a very personal expression, and with small windows in them. They have come with windows along side them (on one or both sides) vertically (called "side lights"), and they have come with double doors (covering an opening of 5'-6' depending on the width of each door).
For interior doors, 36" widths are now quite common and recommended for maximum accessibility. Not only do they allow wheelchair access except for very wide chairs, they accommodate movement of furniture which can be fairly difficult with narrower openings.
For even wider door openings and even more access, slider doors that pocket or slide across the opening ("barn doors") are being used to create door openings of 8' or more. Bypass doors (even with mirrors - a great way to provide a full-length mirror experience in the home and supplement the shorter mirrors found above bathroom counters) can be used in 2, 3, and 4 doors of up to 36" in width to cover a space of up to 12' in width.
Slider, bypass, and pocket glass doors often variety as well - as do transom glass or openings above doors for architectural interest, light, and ventilation.
In many cases, no physical door is needed at all. In such cases, where just a separation of space and a physical indication of that separation but without an actual door that is needs to be opened and closed, a cased opening or archway is a very attractive and practical solution, This offers visual interest and appeal plus allows for very wide openings without being concerned about physical doors being hung in the space and then allowing space for them to be opened.
Doorways and doorway treatments are part of the many building product improvements in recent years (along with flooring, lighting, cabinetry, door hardware, appliances, bath fixtures, countertops, and controls, among others) that have facilitated universal design and aging-in-place solutions.