This info has been taken from another post so credit goes to the original author,I think its Joolay from XDA.
Please feel free to add extra info if needed.
COM1- Builds 217**:
COM2 - Builds 218**: GUI is 1st stage of finger friendly features implemented. This is the only official WM6.5 released to public. All other COM* Builds are leaked test builds (not even classified as alpha or beta). In this range, the GUI introduces softer corners to various dialogs, the new start menu (Very early builds had a honeycomb theme but although the hexagons have been removed, the icon alignments remain), and the taskbar and menubar have been slightly modified to allow for further skinning.
COM3 - Builds 230**: GUI from 23001 to 23021 looks the same as COM2. 23022+ introduced the new shorter/expanding taskbar and finger friendly text-based buttons on taller bottom menubar and ever since its been called wm6.5.1 rather than 6.5..
23047+ introduced icon-based buttons.. New checkboxes and scroll bars and recently (from 23069 i think) a magnifier in the taskbar are amongst the newer gui elements introduced in the latest builds..
At some point (im not sure when, kinetic scrolling was introduced..
It appears that COM4 elements are being introduced into this branch such as the new contact application, a slightly modified sms application, and possibly a slightly modified calender application..
COM4 - Builds 234**: Seems to have stopped at 23420. The newer contact application and possibly the modified sms and calender applications were first introduced in this branch but have since been incorporated into latest builds of COM3
COM5 - Builds 235**: At the moment little is known of this branch. 23502 is the first build leaked that Im aware of. It seems to have been compiled at about the same time as 23060 but with superior stability, speed, memory management, Newer COM3 builds 23071 and above have been reported to be superior in terms of stability and speed. However the latest COM5 23506 compared to COM3 23088 (build date is identical) seem equally fast and stable. COM5 builds have the new Contact app and Magnifier, as in latest COM3 Builds, but lack kinetic scrolling.
Apparently, the new internet explorer has been modified as well (but Bikertibi Builds have the old internet explorer from wm6.1 because new one does not handle well on our device)
Other branches you might or might not come to see:
AKU1 - Builds 212**
SAM1 - Builds 215**
MD1 - Builds 219**
WMD - Builds 28***: The First Build leaked is 28002 (build date 17th November 2009). As of this branch Windows Mobile is at WM6.5.3. This branch is to continue from COM3 23090 and is believed to carry improvements to the New Internet Explorer Mobile as well as overall speed
Builds 216**: leaked builds that have been played with by the team over at HTC but not officially used on any handset as yet
Builds 236**: LG Core Multi Platform Build..continue dev... most builds are fast n stable (improvement starting from 23618)
Big thanks to dragonmatahari for this info !!!!
Windows Mobile 6.1
Windows Mobile 6.1 was announced April 1, 2008. It is a minor upgrade to the existing Windows Mobile 6 platform which brings with it various performance enhancements,
a redesigned Home screen featuring horizontal tiles that expand on clicking to display more information, although this new home screen is featured only on Windows Mobile Standard edition.
This feature was inexplicably left out of the Professional edition.
Several other changes such as threaded SMS, full page zooming in Internet Explorer and 'Domain Enroll' have also been added, along with a "mobile" version of the Microsoft OneNote program
and an interactive "Getting Started" wizard. Domain Enroll is functionality to connect the device to System Center Mobile Device Manager 2008, a product to manage mobile devices.
There are other differences as well. The most prominent difference for the user is that the Standard version (like earlier versions) still creates automatic links for telephone numbers in Tasks and Appointments, which allows for the easier click and dial of stored telephone numbers within these Outlook items.For some reason, the Professional version has eliminated this important feature.
Windows Mobile 6.1 also featured improved bandwidth efficiency in its push email protocol "Activesync" of "up to 40%*"(*source of info : http://blogs.msdn.co...announced.aspx), this reduced data usage was the cause of considerably improved battery life in many devices. Aside from the visual and feature distinctions, the underlying CE versions can be used to differentiate WM6.0 from WM 6.1.The version of Windows CE in WM 6.0 is 5.2.*, with the final number being a 4 digit build ID (e.g. 5.2.1622 on HTC Wing). In WM 6.1, the CE version is 5.2.* with a 5 digit build number (e.g. 5.2.19216 on Palm Treo 800w).
Windows Mobile 6.5
Windows Mobile 6.5 was never part of Microsoft's mobile phone roadmap, and has been described by its chief executive, Steve Ballmer,
as an unwanted stopgap until the multi-touch enabled Windows Mobile 7 arrives in 2010. Version 6.5 is an upgrade to Windows Mobile 6.1 that was released to manufacturers on May 11, 2009,
and the first devices running the operating system debuted in late October '09.
This incremental update includes some significant new added features, such as a revamped GUI, new today screen with vertically scrollable labels (called 'Titanium'); though is generally regarded as a minor upgrade.It also includes the new Internet Explorer Mobile 6 browser (offering an Adobe Flash Lite 3 plug-in to its hardware partners using Windows Mobile 6.5),which has an improved interface over previous versions.
Microsoft unveiled this version at the 2009 Mobile World Congress in February, and several devices now run this Windows Mobile version,devices running Windows Mobile 6.5 onwards are marketed as "Windows phones". Along with Windows Mobile 6.5, Microsoft announced several Cloud computing services codenamed "SkyBox","SkyLine","SkyMarket"."SkyBox" has been confirmed as My Phone, while "SkyMarket" has been confirmed as Windows Marketplace for Mobile.Some aspects of the user interface have been redesigned with the home screen resembling that of Microsoft's Zune player and the sliding panel interface of Windows Mobile 6.1 Standard. This version was designed mainly for easier finger usage.Whilst this version of Windows Mobile does not natively support capacitive screens, mobile manufacturers have been able to successfully implement it on their devices.
Builds of Windows Mobile 6.5.1 have already been leaked and unofficially ported to several Windows Mobile phones.
Windows Mobile 6.5.1 will bring a more finger-friendly user interface, including icon based soft buttons (rather than text based),an updated contacts app, Microsoft (rather than the mobile carrier) support for A-GPS, improved threaded text messaging, and performance improvements.
Windows Mobile 6.5.3
On February 2, 2010, the Sony Ericsson Aspen with Windows Mobile 6.5.3 was officially announced, making it the first Windows Phone 6.5.3 smartphone.
Since November 2009, several 6.5.3 builds had leaked (28nnn) and had been unofficially ported to some Windows Mobile phones. Windows Mobile 6.5.3 brings a more finger-friendly user interface with several new ease of use features such as support for multitouch, complete touch control i.e. no need for a stylus, and drag and drop start menu icons. Touchable tiles now replace soft keys."Internet Explorer Mobile 6 has also received some major updates including decreased page load time, improved memory management and gesture smoothing. Additional features of newer Windows Mobile 6.5.3 builds include threaded email and Office Mobile 2010.
Windows Mobile 6.5.5
Several builds of Windows Mobile have leaked since January 2010 and have been unofficially ported to some Windows Mobile phones.
The name Windows Mobile 6.5.5 has been applied to these newer builds. However, this naming scheme remains unconfirmed by Microsoft.
Future versions : Windows Phone 7
Microsoft had originally planned to continue the Windows Mobile line to Windows Mobile 7, based on an upgrade to the Windows Mobile platform codenamed Photon.
The original Photon and Windows Mobile 7 have since been scrapped, however Microsoft has officially announced Windows Phone 7 Series in its place.
Microsoft has since also renamed the operating system from Windows Phone 7 Series to Windows Phone 7.It is planned for release by "holiday" 2010.
Windows Phone 7 was initially intended to be released during 2009, but several delays, and likely due to the move away from Photon, prompted Microsoft to develop Windows Mobile 6.5 as an interim release. During the Mobile World Congress 2010 in Barcelona, Microsoft revealed details of Windows Phone 7, which features a new operating system and integration with Xbox Live and Zune services.
It's being said that phones running Windows Mobile 6.x will not be upgradeable to Windows Phone 7.
hopes that helps
Edited by Paul, 03 September 2010 - 02:05 PM.