The very first thing I thought of when I heard about this was Tegmark (mostly from reading the scifi books "Godplayers" and "K-Machines").
For an overview, skip to: http://en.wikipedia.org/wiki/Multiverse#Multi-domain_universes_.28Ellis.2C_Kirchner_and_Stoeger_sense.29:
There are basically 4 levels:
1. The physical constants of the universe (whatever they may be) are set, but all possibilities exist.
2. Same as 1, but now we also have all possible variants of the universe (by varying constants)
3. Reality does not consist of different universes realizing all possibilities - but instead the universe itself branches for all possible quantum variations.
4. Different mathematical laws = different to anything we understand reality to be.
To me it felt like there was a certain amount of overlap with the lower levels, in that semi-plausible values of Cuil (say, below 3, though some of that would be very unlikely) could exist within levels 1 and 2 of Tegmark.
Tegmark 3 is very powerful in that it states that no matter how unlikely, if there is even the slightest chance of an event happening, it's realized.
Tegmark 4 would pretty much cover anything else.