Game System
We will be using Trail of Cthulhu. I'll send out a copy of the rules to players once they have a working character concept.
I am partial to point-budgeting systems like ToC (for reasons explained in part 4 of Kubasik's Interactive Toolkit, under "rules") and the time constraints of an online game like this mean that the less die-rolling and missed clues at critical points the better.
We will use Invisible Castle for whatever die rolls may be necessary.