Just an interpreter executable as Perl, PHP, TCL etc...
well, why not... but it has been created to use with mIRC.
I don't know how you're going to implement an ON TEXT event without mIRC...
Remember Khaled's aim is to create an IRC client, scripts are a "plus".
Anyway mIRC script language is similar to the 3 others so you could use one of thoose.
I'm sure mIRC will be open source in a future, and your mIRC's interpreter will exists