which service provides user account synchronization on a mixed platform enviorment?

Could you clarify your question? Do you mean an a LAN or the Internet?

If you mean on a LAN you can use LDAP to access the user system, and more, to request user account information (for instance what groups/OUs they are in, email addresses contact info etc).

EDIT:

Ok this is a very compex thing to do but it is pefectly possible to get windows domain systems and, for instance UNIX NIS systems to 'replicate' data to each other.

have a look at http://books.google.co.uk/books?id=05xyiZqC8ToC&pg... page 261-299 covers Windows <--> Unix interoperability

Another option is to write a script so that you add/modify/delete items on one system within the script it also adds/modifies/deletes items from the other systems, using LDAP, although this is not to replication/sycronisation and I would recommend also running another script on a schedule, to compare relevant parts of both structures and notify you of any differences. I am sure there must also be seperate 3rd party software out there to do this, but I am not sure of any currently

Not sure about user synchronization, but SAMBA will allow file sharing and printer sharing across multiple platforms. For example, you can set up a fileserver on a unix box and when a windows user attempts to mount, it will know who he/she is and send to correct file area, in effect using same windows credentials...

read more:

http://us1.samba.org/samba/what_is_samba.html

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