There are few GitHub repositories written in Swift that are presented to be "Linux Ready". The Zewo organization has several repositories identified as "Linux Ready". What, exactly, does this mean?
At least according to a quick web search, the expression "Linux ready" does not appear to be some sort of official designation for Swift projects. It looks like only Zewo uses it in that context.
According to the project's README.md, it simply means that the project should work under Linux once a Swift implementation is available for Linux:
Foundationdependency (Linux ready)
So "Linux ready" seems to indicate that the project does not use the Foundation framework, which presumable will not become available under Linux in the foreseeable future.
Related question from StackOverflow: Is it possible to build Swift 2.0 code using the Foundation Framework and target linux?