They're talking about the server, not the client. The client is not available on Linux.
From the url below : Lotus Domino R5 for Linux/x86 has gone Gold ! This release further demonstrates Lotus' commitment to supporting Domino on multiple platforms and continues the strong momentum Linux has generated in the enterprise community. By adding Linux to its existing platform portfolio, Lotus is further differentiating itself from competitors and allowing customers to select the platform that best meets the needs of their unique network and application environment. The Gold beta is available for download now.
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