PostItNotes: TradeName? describing a series of [usually] small, light-colored papers that have lightly adhesive strips at the top of the back side.
PostIt's have many software implementations:
MacOs users have a similar product called Stickies (part of the OS). It doesn't have all the fancy bells and whistles (like alarms), but users generally use a PIM (PersonalInformationManagement) system for that.
WindowsSeven users have StickyNotes.
My computer runs 24/7. I used to use a plain text file for personal notes. I've started using Gnome's Sticky Notes applet for it, but the UI is such that you can only show and hide all notes at once. I'm finding it's just completely unsuitable for dealing with more than just a few notes. Bleh.
If I find something useful on a web site, I tend to just leave it open. The combination of tabs, and Galeon's session recovery has allowed me the terrible, terrible habit of keeping hundreds of pages open pretty much indefinitely, even through power outages. This got me banned off the wiki once, a year ago... -- CallumLerwick
I use Webnote (http://www.aypwip.org/webnote/) for some time. It's online and browser-based and has all the features I need... -- FrankSpychalski
See: IsAnythingBetterThanPaper, HasWantedPages?