I'm trying to set a timer on macOS to no avail, as Siri prompts me to set a reminder instead:
Most, if not all apps found on the Mac App Store don't provide this functionality without being too complicated:
Are there any other apps that can provide the functionality without being too complicated or hard to use?
This free and open-source Timer app seems pretty clean and simple. It can be downloaded as the zipped file Timer.app.zip in the Assets list on the Releases · michaelvillar/timer-app page at GitHub.
It can also be installed using brew:
brew install --cask michaelvillar-timer
Update: MacOS Ventura (13) introduced the in-built Clock app which works like the one on iOS - providing for Alarms, World clock, Timers and Stopwatch.
cd into base dir and run make
Commented
Jul 22, 2020 at 19:38
2 key
Commented
Apr 22, 2022 at 13:33
Here's a little timer shell function. Paste this into Terminal (after you read it and understand it, as always, because pasting random commands from the Internet into Terminal is dangerous):
setalarm() {
sleep $(echo "$1 * 60" | bc)
say "Beep boop"
}
setalarm .1
That's 0.1 minutes (in other words, 6 seconds).
If you want to make the alarm repeat until you press Ctrl+C, then paste this instead:
setalarm() {
sleep $(echo "$1 * 60" | bc)
for x in $(seq 1000); do say "Beep boop"; sleep 0.5; done
}
setalarm .1
say "Beep boop" (in the first function; don't want 1000 notifications) with osascript -e 'display notification "Lorem ipsum dolor sit amet" with title "Title"' as described here (thanks @grg)
Commented
Sep 3, 2021 at 3:17
osascript -e 'display notification "'"$1 minute timer complete"'" with title "Ding!"'
Commented
Sep 3, 2021 at 4:31
function olt() { secs=$(echo "$1 * 60" | bc); msg="${@:2}"; sleep $secs && say $msg & } . With this in my .bash_profile, I can do $ olt 0.1 ok stop doing that. and carry on with the term. Cheers! z
This isn't necessarily a regular MacOS application, but if you are alright with using the Terminal, termdown is a really nice Terminal Stopwatch. Starting a timer is very simple. For example, termdown 1h30m starts a 1 hour 30 minute timer. 
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The built-in leave command is handy for this sort of thing.
Set to alert after 1 minute:
% leave +0001
Alarm set for Wed Jun 23 20:42:22 HST 2021. (pid 15321)
Set to alert at 8:45 PM:
% leave 2045
Alarm set for Wed Jun 23 20:45:00 HST 2021. (pid 15323)
kill <pid of leave here> or killall leave
I wrote a countdown timer called Super Easy Timer every day for my Pomodoro and writing work sessions.
It can recognize natural language, so that you can set the timer by typing "20 minutes" or "2 days 20 hours and 13 minutes".
You can also update the timer on the fly, or reset it with a keyboard shortcut. (Command + R)
And if you have an upcoming meeting, or happy hour, you can type "5pm" to get a countdown to your next event.
You can try the timer here, or you can download it from the Mac App Store.
There are keyboard shortcuts and natural language here:
Disclaimer: I created the app because I wasn't happy with the other timer apps I found. I wanted a quick, simple to use, and reliable timer app.
Dont know when they introduced it but macos has an app on board. 
I like to use Horo. It's a status bar app
You can use timeanddate.com to set a timer.
This utility also includes multiple sounds that will play when the timer ends.
It also has other time/date-related utilities as well.
Open any modern web browser (Chrome, Firefox etc), go to google.com and enter "timer" in a search box:
It does a nice beep at the end.
PS. I entered this as an answer here because I had the same question, googled it, stumbled upon this page, and after reading it all ended up using the solution I just proposed, because it was the simplest.
Try this: https://www.apimac.com/mac/timer/
It has a clean and easy to use interface. It can be used to start multiple countdown timers, stopwatches as well as set alarms.
You can also set simple tasks instead of just an alarm tone like, open an application or read out some text, etc.
I use http://www.timer-tab.com and I love it. I don't need multiple timers so its effective at doing its job and staying out of the way. You can run it in your browser. You dont need an app since its web based.
I use a countdowm timer that works great and is simple. It's called Countdown Widget and you can select to countdown based on days or time. I'm currently using it to countdown days till baseball season starts again. But it will countdown in seconds as well.
There is a built-in(?) ShortCut called "Start Timer" (found via Spotlight) that goes and sets it quickly.
This little script might be useful for small tasks.
Copy & Paste in the Terminal
alias timer='for i in `seq 1 65535`; do sleep 1s; clear; echo $i $( echo Seconds ) ;done'
Type timer
