a) According to the faq it implies that Lazarus can even run on a Mac ( I assume if Max is running on Intel chipset only) As far as I know the new Macs are really a copy of an older Debian that Apple copied and made a few changes and some cosmetics layered on top and wrapped it up in shiny Apple paper and branded it as Mac OS.
At least Free Pascal is also is able to run on PPC powered macs. There is a
mac portal on the wiki and
MacOS X installation tips (which includes a compatibility matrix).
Here is a list of supported targets.
b) Does an Lazarus app / program run fast enough on a Mac, Linux and Windows.
Is it really mainly write one and compile and run it ok, as long as you do not too much "system" stuff. and write most portable code?
Yes. At least Free Pascal is able to produce code that also runs on Win 3.11, MS-Dos, Atari and Amiga for example. Lazarus (read widgetset) is a bit harder for those (outdated) platforms.
If you separate the GUI from actual code it is always possible to easily add support for native GUI (if there is any available).
There is a wiki-page on
multi-platform programming with FPC/Lazarus.
C++ or cpp in bgi (Borland graphics interface?),
Yes that stands for Borland Graphics Interface. I would advice against using it although possible with FPC.
cpp in mfc (ms foundation class?)
Correct, not portable as it is windows only so requires a rewrite.
and cpp in something like owl (object windows library? (Borland or ms?)
owl is outdated, requires rewrite. Borland had support for that with Turbo C/Pascal for Windows.
Can you give me advice on some documents or web pages to read to port old code?
My advise would be to do a rewrite. The things you mention is really old stuff. that it isn't worth the effort. If you have more actual code that isn't tight to the GUI then you can ofcourse easily transfer that to Pascal code. GUI bits would have to be rewritten/redesigned (but that is easy to do with Lazarus RAD design).
c) would Lazarus be a better choice than python
In my personal opinion, yes. But i do not like python very much but i also use(d) TP/BP/Delphi for ages, so am a bit biased
d) is javascript a better choice to do everything in a "browser application"?
No opinion on that subject other then to say that if that is your aim (run everything in the browser) that FPC/Lazarus might perhaps not be the best of choices.