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Aurora looks good, maybe a lil memory heavy. so far i dont think it has the option for a message to show along with the alarm
 
you can put date/times with alarms in calendar. personally I use my iPhone as my alarm clock.
 
I don't think it's impossible: In the create an alarm window, there's a place "Run: Drag application or file here". For that, you could make an applescript file to prompt a message of choice.
About the memory usage I don't know, I use it occasionally but I haven't monitored its consumption. Well, at least I haven't experienced it slowing down my computer in any obvious way.
 
I have been using this Alarm Clock application since 10.5 or so. Sadly, it does not seem to be generally available anymore, so I have attached it here. It still works great on Yosemite.

It runs in the menu bar, lets you do timer, alarm clock, or stopwatch. It lets you choose a song for the alarm with gradual volume increase. It was free when it was available, and I still have not found a better alarm clock application for the Mac.
 

Attachments

  • Alarm Clock.app.zip
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i think im using the same, its simply called "Alarm Clock" - works good, menu with clock pic nicely in the wifi/volume area of the top men. all its missing is option to show a message, in case u cant remember what u set the alarm for
 
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