Stealth software that will pop up messages at future dates?

A very dear friend of mine leaves on Wednesday for a world tour taking her through parts of Europe, the Middle East, and SE Asia. She has bought a new compact laptop to bring on her travels, and I have it in my possession as I’m getting her all set up with the variety of softs she’ll need on her journey.

Wondering if anyone knows of something that I could install that would run in the background (with minimal use of resources of course) that could pop up messages at pre-determined times (on my birthday, Christmas, etc), showing up on the screen on the date or whenever it is next booted thereafter?

A little quick Googling reveals the following (I’m assuming your OS is Windows):

I haven’t used any of these programs, but all of them look to be able to do what you need.