Here is a list of all documented namespaces with brief descriptions:

NArchive_Zip
Nclass
Ndatabase
NEasyLexSQL
Nkernel	This version uses XOOPSCube XCube Delegate
NLegacy	This file declares some structure-class and stored-system readers for the installer
Nlegacy
NLegacyRender
NlegacyRender
NMessage
NPreload
Nprofile
NShadePlus
NShadeSoap
NSitemap
NstdCache
NUser
Nuser
Nxcat
NXCL	This file was entirely rewritten by the XOOPSCube Legacy project for compatibility with XOOPS2
NXCube	If the first character in a line is #, ; or //, the line is treated as comment
NXOOPS2	This file defines constants which were defined in system module of XOOPS2. Legacy module already has removed all codes which depend on these constants. This file may be loaded by some developers who need these constants
Nxoops2	This file has been moved from XOOPS2 for some things which need full-compatibility with XOOPS2