Citymapper
citymapper.com
Public-transport directions that tell you which carriage to stand in
No sign-up
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Routes, flights, time zones and places worth seeing.
citymapper.com
Public-transport directions that tell you which carriage to stand in
flightradar24.com
Shows aircraft moving in real time, with the tail number and where it came from
komoot.com
Plans a cycling or hiking route by surface, gradient and what other people ride
marinetraffic.com
Live positions for merchant ships, ferries and yachts broadcasting AIS
openstreetmap.org
A map of the world anyone can correct, and everyone else can reuse
passportindex.org
Shows where a given passport gets you in without applying for a visa first
randomstreetview.com
Drops you at a random street-level spot anywhere Street View has been
rome2rio.com
Answers how to get from any place to any other place, by every mode at once
seat61.com
One man's hand-written guide to reaching anywhere by train and ferry
windy.com
An animated weather map you can scrub forward hour by hour
worldtimebuddy.com
Lines up several cities' clocks in one strip so you can see the overlap
By task
Archive
Kept on record so an old bookmark still leads to an answer. Each one names the site that does the job now.
tagzania.com
Tagged your own places on a shared map and published them as a collection
Questions
There is no single answer, which is why this page lists 11 of them with their limits stated. If you want to avoid signing up entirely, 8 of these work with no account at all.
Every site in this category sends your input to its own server to do the work. That is fine for public material; for anything containing personal data, check the on-device collection instead.
Some already have. 1 entry in this category has been retired and moved to the Archive with a working successor, so an old bookmark still leads somewhere useful.