This place is most things about SAP.
It's DAVID's knowledge base to summarize his knowledge of SAP during work.
If you also wanna build it to share your knowledge togerther with me here, please just mail blueoxygen at gmail.com.

My Functions lib

• GUI
• File Manipulation
• String
• Excel
• Date&Time
• System
• FI/CO
• MM&PP
• SD
  

Others

• Amazing Function list(by category)

• Useful Function list
• Most used Functions
• List of ABAP Functions(1)(2)(3)