What are reminder extensions, TIMERS for Google Chrome/Opera?

Question

Opera

Which would be reminiscent of the event.
With function
1. Add a timer (task) give it a name.
2. Set the date, time of notification (graphic and or sound signal)
EVERYTHING !!
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Installed different ones but they did not work.......

Answer 1

www.onlinetimer.ru - if it's about short-term.
And so put all sorts of calendars, the same Google, and turn on push notifications