Flux Scripting Language

Could support commands like the following ...

gold = 1
gold = gold + 1
add "key" to bag
remove "key" from bag
if key in bag then door = open
if gold = 5 then message = "You are rich"
unless door is open then message = "Door is closed"
message = "Kilroy was here"

Or shorter

gold += 1
bag += "key"
bag.key ? open = 1 : open = 0

Define a subset of Ruby to support it?
Other language? Lua?
Define a custom language using TreeTop
Datatypes; Integer, Boolean, Set, Dictionary
Simple conditionals; if, unless, case
Create a Ruby play object where all code is executed with. Store complete state to database after each evaluation. Allow only object instance variables that can be marshalled.
Script code may be included in page contents

References

twine - compare with interactive fiction game engines
ChoiceScript