Is there a format better than CHM to integrate to Lazarus as an offline help?
Yes, INF help files and viewable with DocView. fpdoc can generate IPF output, which you then compile to highly optimised INF help files using the WIPFC compiler - a stand alone console tool included in the fpGUI code repository.
DocView is better than any CHM viewer I have come across. It is much faster at starting up (near instant) and loading INF files. You can load multiple INF files at the same time too (runtime concatenation of INF files), supports inline annotations, advanced searching with a rating system, and runtime building of Indexes, font and colour customization etc. DocView is also fully cross-platform, tested under Windows (win2k-win10), Linux, FreeBSD, Solaris and OSX.
Authoring help for your own applications (not class documentation):I use the text editor called EditPad Pro. It has brilliant code template support, live file navigation and customisable syntax highlighter. A IPF syntax highlighter and navigation scheme is freely available on the EditPad Pro website. But any text editor (even Lazarus IDE) can be used to author INF help. The IPF syntax is easy and the tags are mnemonic based, so very easy to learn and associated with their function - it is also much less verbose than HTML or XML.
INF was originally developed by IBM, but is still an excellent (and relevant) choice today. Especially with the much more feature complete DocView INF viewer (compared to IBM's original VIEW application).
Even though Docview was initially written for fpGUI based projects, it works equally well as an eBook type application or integration with LCL based applications. Here is a link to a forum attachment of a fully working LCL application with DocView+INF incorporated. For the full discussion, see the Lazarus Forum post.
http://forum.lazarus.freepascal.org/index.php/topic,27864.msg173887.html#msg173887Docview screenshots: http://fpgui.sourceforge.net/screenshots_apps.shtmlDocview pre-compiled binaries: http://sourceforge.net/projects/fpgui/files/fpGUI/1.4/INF help files for RTL, FCL, LCL and fpGUIPre-built INF files are available for download from the above SourceForge link too. They are also a fraction of the size of HTML or even CHM - yet contain the exact same help content.