Microsoft has so many rivals it's hard to even figure out which ones are most likely to keep CEO Steve Ballmer up at night.
Microsoft seemingly tries to dominate every software market in both the consumer and enterprise landscapes. Windows and Microsoft Office would be enough to sustain most vendors, but Redmond wants more: databases, cloud computing, e-mail, search, virtualization, unified communications, Web browsers, mobile phones and tablets, even video games.
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Sometimes, Microsoft blurs the lines by forming tight partnerships with competitors, as it has done with Citrix and Yahoo. Here, we'll focus on the rivals we think pose the biggest threat to Redmond and give a status update on each rivalry.