Project Mono 1.0

"Mono 1.0 will not emulate all the functions currently in the .Net Framework, such as Windows Forms or enterprise services such as message and transaction queueing, de Icaza said. It's not clear yet whether it will feature support for SOAP (Simple Object Access Protocol), for letting applications running on different platforms to communicate, a key ingredient for Web services applications."
[InfoWorld]

Looks like you'll have to wait a bit longer...