XDADeveloperWiki - Windows CE

Windows CE is the name of the operating system that runs on the Pocket PC or Handheld PC platforms.

The different OS versions and platforms are as follows:

Windows Mobile 6 Standard, Classic and Professional	Windows CE 5.2
Windows Mobile 5 for Smartphone/Pocket PC	Windows CE 5.0
Windows Mobile 2003 for Smartphone	Windows CE 4.20
Smartphone 2002 (V1)	Windows CE 3.00
Windows Mobile 2003 for Pocket PC with/without Phone Edition Software	Windows CE 4.20
Pocket PC 2002 Pro/Premium/Phone (P/PC V2.1)	Windows CE 3.00 (3.0 networking)
Pocket PC 2000 Std/Pro (P/PC V2)	Windows CE 3.00 (2.12 networking)
Palm-size PC V1.2 (Color P/PC)	Windows CE 2.11
Palm-size PC V1.1 (Chinese P/PC)	Windows CE 2.01
Palm-size PC V1	Windows CE 2.11
Handheld PC 2000 (V4)	Windows CE 3.00
Handheld PC Pro (V3)	Windows CE 2.11
Handheld PC Std (V2)	Windows CE 2.00
Handheld PC V1.1 (Japanese H/PC)	Windows CE 1.01
Handheld PC V1 (original)	Windows CE 1.00

(Source: this page)

Windows CE.NET is a name applied to all Windows CE versions of 4.00 and higher.

More information is available here.