Visit the SCI Companion for download links and more info: SCI Companion 3
I've spent much of the last year working on version 3 of SCI Companion, which now provides full support for creating and modding VGA Sierra games. It even includes a decompiler to reconstruct source code from old games!
blurb from my website:
SCI Companion is a completely free IDE (integrated development environment) that lets you create games that run on Sierra’s SCI engine. SCI Companion 3 is now available, which offers support for SCI1.1+, which includes VGA graphics and digital audio.
Create 16-color EGA graphical adventures with a text parser interface (in the style of King’s Quest 4, Space Quest 3 or Leisure Suit Larry 3).
Create 256-color VGA graphical adventures with a point-and-click interface (in the style of Space Quest 5, Gabriel Knight, or Quest For Glory 3).
Comes with a complete well-documented class system and template game.
Lets you browse, extract or modify graphics, text and sounds from nearly any SCI game that you own.
Decompile the code behind these classic games to see how they work (or find Easter eggs). Scripting in SCI is accomplished via a language similar to LISP and SmallTalk.
Includes streamlined editors for graphic assets.
And other game resources like text and audio.