Kismet

Kismet is visual script editor embedded in UnrealEd. It allows you to create scripted sequences in an intuitive way by mean of connecting various nodes (actions, variables, events, …) with lines that describe exectuion or data flow. It works for most level design related tasks and so it shields UnrealEd user from raw UnrealScript.

Check Kismet Editor Reference for further information.

Resources

AVLD Kismet Tutorials
Kismet Tutorial on UDN beta
Kismet (gameplay scripting) on Wikipedia