Better link:
http://www.gamasutra.com/gdc2005/features/20050315/postcard-diamante.htm

Will Wright's Spore is a bit similar to Croquet on these points:

1. Multi-user, synchronized, 3D environment - scaleable by both number of users
and zooming from the macro to the micro in the 3D space
2. Algorithm created content (optional in Croquet)
3. User created content is the best content because it encourages "ownership"

Spore advantages over Croquet:

1. Everything is algorithm generated so it’s fast, compact, easy to distribute.
2. Ease of 3D content creation due to predefined pallet of construction
resources from which to choose
3. Physics is automatic and inter-object physical interaction behavior is
extrapolated at runtime
4. Hard to reverse engineer, so easier to protect Intellectual Property if you
have any
5. Efficient generation/memory-storage of textures
6. All 3D content exists in one single universe, so all content can be located
by a single 3D position in the universe for it
7. Articulated avatars with preprogrammed, realistic motion & behavior
8. Hard for the user to crash the system
9. Less need for security to insulate users' behavior from each other

Croquet advantages over Spore:

1. Not all content can be expressed by algorithms, especially in education,
where the domain to be learned has already been expressed in other multimedia
2. Users can create their own programming logic/behavior as well as their own
content
3. Lots of new non-algorithmic content can be created
4. Open source
5. Easier to enhance with add-on extensions which are automatically distributed
6. Hard to derive content from algorithms, so hybrid approach helps in
transition
7. Can easily record and play back the user stories in dynamic or other
multimedia
8. Easy to reverse engineer, so easier to enhance or build the next big thing
9. Multiple user-created worlds can exist separate from each other, so easier to
focus on specific communication activity or learning activity, and easier to
create/duplicate a world & its content
10. Can search content data for values, labels, or code used by the active
content
11. Can represent the chemical tools of biological organisms as well as
structural tools

I'm sure others can think of more advantages and disadvantages.