[Touch GSM ROM Development] trueg:
SYS - very often you don't need to make many changes to this, unless you need to change the language or would like to make changes to default settings (like the font size for example).

ADC - Automatic Data Connection wizard - automatically configures your data settings based on your SIM card. It works great for me (Rogers Wireless in Canada), but it may not work for you. Some people prefer HTC connectionsetup. Feel free to delete both folders.​

AdobeFlash - Adobe Flash Lite - Allows IE to render web pages with Flash. Works well for animations (example www.homestarrunner.com), but a bit slow for video (youtube). Delete if you no longer want to support Flash.​

AutoUpdate - Windows Mobile Autoupdate - can be removed assuming you keep packageinfoapi.dll (mentioned by !Aman! on the previous page).​

Base* - WM OS files - do not delete any of these folders - various changes can be made to the RGU files if you know what you are doing. There are also several files that can be modified or deleted, but there are too many to cover here.​

Bluetooth - Windows Mobile Bluetooth stack​

Bronze* - Titanium CPR files and graphics​

Browsing* - Windows Mobile Internet Explorer​

BTDUN - Dial-up Networking Profile for Bluetooth​

Bth_A2DP* - Advanced Audio Distribution Profile for Bluetooth​

Bth_HID - Human Interface Device Profile for Bluetooth​

CHome* - Titanium drivers and settings​

CommonNonEA - contains a single registry setting pertaining to Inbox Recipient Autocomplete​

ConfettiCore - do not delete - required by Titanium, Lockscreen & Shell32​

DRM - default WM DRM driver​

Enterprise* - several of the folders are empty, but the main folder contains the drivers and settings for NDIS & IPSec​

Entertainment* - contains the games BubbleBreaker & Solitare - often deleted​

FWUPDATE* - allows for over the air ROM updates - not currently supported - can be deleted and replaced with dummy package​

GPSID - contains the default GPS driver​

InternetSharing - WM Internet Sharing - Allows you to share your data connection with another device (example: laptop).​

IPSECVPN - core drivers for IPSec & VPN​

IRDA* - drivers for Infrared adapter - can be deleted unless your device actually has an infrared adapter. The ELF does not.​

Lockscreen - drivers, graphics & CPR files for the new Lockscreen included with WM 6.5​

MediaOS - drivers & resources for Windows Media Player Mobile​

Metadata - registry & certificate resource files​

NetCF - .Net for Windows Mobile - WM 6.5 SDK still includes version 2.0​

Office* - Microsoft Office Mobile​

OneNote* - Microsoft One Note Mobile​

OS* - Windows Mobile 6.5 core OS drivers & resources​

Phone* - Drivers, resources & ringtones for Phone support - needed for Phone support, but resources for the dialer, call history & speed dial can be changed.​

ppgprov - contains a single provxml that sets up the WAP push gateway for SMS​

Redist* - contains a lot of OS applications & resources​

RUNTIMES - OS Runtime libraries (for example MFC for C++)​

SampleMusic - contains the default songs that come with Windows Mobile - I usually delete this folder​

Shell - more core OS files - do not delete - the RGU contains many useful registry settings​

SIM_TKit - used for loading SIM card apps - possibly required if you use a Super SIM​

Skybox - Microsoft MyPhone - Allows you to back up SMS, documents, music, etc online. Actually pretty useful.​

Skymarket - Windows Mobile Marketplace - Has yet to launch​

SMIME - Email encryption driver​

SMS_Providers - driver & registry settings for SMS​

SQL* - SQL for Mobile​

SQM - System Quality Metrics - Used in conjunction with Error Reporting - often deleted and replaced with dummy custsat.dll​

Themes* - contains TSK files & resources for the default Themes​

Transcriber* - Windows Mobile Transcriber SIP - handwriting recognition software​

VoiceCommand* - Voice Activated Control/Input System - I find it works very well and use it while driving, but not everyone likes it.​

WelcomeCenter* - Welcome Center Wizard that provides assistance in doing basic tasks - I always delete this​

WinCENLS_WWE - National Language Support file - gets replaced if you port to a different language.​

WindowsLive* - Microsoft Windows Live Mobile - provides interface for Windows Live & IM.​

WMLiveSearchWidget - Live Search Widget - feel free to delete - other Widgets like MS Money & MS Weather can also be found here on XDA.​

WMWidgets* - drivers & resources to support Widgets​

WWAN - contains wwan.dll & registry entry - can't find much info on it, but doesn't seem to be of much value.​