Right off the bat I want to say that both when and remind are excellent pieces of software.
Common to both are that they are CLI applications, light on resources, and store data in plaintext formats.
They differ in syntax and through that they differ somewhat in complexity, and, although unconfirmed, this may also affect their individual capabilities (i.e. the more complex the syntax, the more time to learn it, but the more powerful the expressions).
Of the two I found out about when first, but I can’t for the life of me recall when or where I first read about it. It may very well have been through StumbleUpon.
remind, on the other hand, was recommended to me some time ago by my very good friend bumby.
Comparing their different syntaxes might be the best way of showing off their differences:
We’ll start with something simple, like a notice to remember the fifth of
November:
when syntax:
* 11 5. Remember, remember, the fifth of November
remind syntax:
REM Nov 5 MSG Remember, remember, the fifth of November
Or, let’s say you want to be reminded to celebrate the birth of the Epoch, and know how “old” the Epoch is now.
In when syntax, that would be expressed as:
1970* 1 1, The Epoch is now \a years old
the same expression would, in remind be:
REM Jan 1 MSG The Epoch is now [year(trigdate())-1970] years old
Now, truth be told, I have created an expression in when which I am not sure I could (or as I probably can, how I would do it) in remind:
y=2010 & m>=4 & ((m=11 & d<6) | (m<11)) & (d=1 | d=11 | d=21), #FSCONS2010, #fscons@freenode, 14:00
During the planning of FSCONS 2010, we had meetings at 14:00 hours the 1st, 11th and 21st of every month between April and November. This expression kept me on track.
I guess I can rest assured that bumby will spend all night coming up with the equivalent expression for remind 
Since I while back I decided that remind was the right choice for me. What was the killer feature which had me leave when for remind? Well, truth be told, the feature isn’t in remind at all.
The one thing I lacked in when was some sort of graphical “calendaric” view. Sure, in a pinch cal will do the job, but I wanted something more flexible, something more interactive, something more like… calcurse.
The only problem? calcurse stores appointments in a file of its own, in a different format, and even if I had acted on my initial urge to write a converter between the two formats, I would still have been in violation of the DRY-principle.
This problem doesn’t exist with remind, as there exist a software almost identical to calcurse named wyrd, with the one crucial difference: where calcurse store appointments in a format of its own, wyrd operates solely on the files used by remind.
So was it worth it? Switching from a syntax I fully comprehend, to a more complex one which will take me a while to learn? A switch which also meant having to rewrite the Important Dates Notifier-script? In the long term? Yes, it will be worth it. In the long term, complexity will turn into power, as I begin to better understand the syntax, and become able to fully utilize it.
But for anyone with a brain wired like mine (thinking the FSCONS-meeting example above made perfect sense), who can live without any additional power/complexity, I still warmly recommend when. And if you need that power, have a look at remind. It might be just what you need.
:wq
