Windows Mobile 5.0, originally codenamed "Magneto", was released at Microsoft's Mobile and Embedded Developers Conference 2005 in Las Vegas, May 9–May 12, 2005. Microsoft plans to offer mainstream support for Windows Mobile 5 through October 12, 2010, and extended support through October 13, 2015. It was first offered on the Dell Axim x51. It used the .NET Compact Framework 1.0 SP3 — an environment for programs based on .NET.
Source: Wikipedia