Apple has their own tablet in the iPad and Google is said to working on their own iOS tablet which will be launching this summer by most accounts.
Microsoft however has stayed out of the hardware side of the tablet business, placing their focus on the operating system that runs a Windows tablet. However, there is a good chance that all of this will change next week with insiders claiming that Microsoft will announce their own tablet on Monday. This announcement is expected to become official on Monday, June 18th at 3:30 local time. Although we may have some insight as to the timing of the event, in terms of the location, this is not clear. The announcement will take place in Los Angeles, but the actual location within the city is unknown at this time.