Continuing from the http://www.gamesas.com/topic/1479430-rel-oblivion-script-extender-obse-0021/

OBSE - The Oblivion Script Extender
OBSE is a modder's resource that expands the scripting capabilities of Oblivion.

It doesn't make any modifications to Oblivion.exe, TESConstructionSet.exe, or any other files in your Oblivion install, so don't worry about permanent side effects. As of v0017, OBSE requires the 1.2.0.416 version of Oblivion.

http://obse.silverlock.org/download/obse_0021.zip - current stable version, recommended for general use
http://obse.silverlock.org/
http://obse.silverlock.org/obse_command_doc.html - link is for v20 documentation. v21 documentation is included in the download.

What's new:

Readme (abbreviated):

For mod developers:
http://oblivion.nexusmods.com/mods/36370 - An OBSE plugin that fixes bugs in the CS and adds new features to it