SPList Event Receiver with which you can trap changes to the fields of an existing list as well asactions related to adding or deleting lists instances.
The Events Provided by the SPList Event Receiver Base Class Field Added Occurs after a field has been added to a list definition.
After events ( Asynchronous) are those that happen after Share Point commits the data to the Share Point content database After events by default run in a background thread; however, you can force them to run synchronously Example: Item Added Occurs after an item has been added to a list.
Another limitation of v2 event handlers is that you can only catch events on document and forms libraries. Now, WSS v3 has a vastly increased number of events developers can take advantage of.
These events include "before the fact" or synchronous events as well as "after the fact" or asynchronous events as illustrated in Figure 1.
(like all those events that are having “-ed” as suffix).
As far as After Properties and Before Properties are concerned for any event, they can help you to extract After and Before change in state about the object in context.
As a developer interested in catching Share Point events, you are no longer limited to only document libraries and forms libraries.