Short answer

• MAC OSx: yes.
  MZ3 titles run in a browser with Flash support as Online version. A projector (Offline version) can be built using the megazine.app file/folder also. 
• iPAD/iPhone (iOS): most probably yes
  Flash is not supported by those devices,  but Adobe AIR is. With the support of that framework MZ3 titles can be viewed on those devices also. So far in theory only, because we did not prove it works under iOS and AIR ourselves yet.
  We tested it on Windows and AIR, and it works.

Long answer

MZ3 "Development"

• The basic way: An editor and swftools
  To create/build a book, any text editor will do it. 

  The configuration of the megazine.mz3 file (which is an XML format) can be done on a MAC also.
  On Windows we suggest a context sensitive editor like notepad++ (free) or XMLBlueprint (commercial version for about $80).
  On a MAC there will be options also, but we do not have personal experience. Please check the list of editors provided here:
  http://en.wikipedia.org/wiki/Comparison_of_text_editors
  http://en.wikipedia.org/wiki/List_of_text_editors
  
  Aquamacs seems to be very powerful, MAC based and free:
  http://en.wikipedia.org/wiki/Aquamacs
  http://aquamacs.org/
  Since we never worked with it, this is not a recommendation but only a suggestion to check it out.
  
  For tests you can download the demo book to get an example of a "real" megazine.mz3 configuration file and do some tests with your editor of choice.

  To convert a PDF file into swf pages, that are needed for MegaZine3, you need to use the tools available from swftools.org, or use a commercial tool like iFunia (not tested; no recommendation, only for info). Or again use a Windows system for that purpose...

  Summary: You can build your MegaZine3 titles on a MAC. Also the PDF conversion can be done on a MAC (somehow).

• The comfortable way: Batch Command Tools
  

  On a Windows based system there are tools available as part of the demo package that help building megazine.mz3 files and the related index files automatically. And also create the suggested folder structure.
  Even the PDF conversion is done in the background without the need of user interaction.

  A compromise for MAC users could be to run the "tools" once on a Windows system (Desktop, Laptop;  or as alternate boot on your MAC) and create a personal "best fit megazine.mz3 template".
  With that template all future books can be built on a MAC with the editor of choice; and a little experience about the logic and structure of MegaZine3 files.
  You'll learn it fast. Especially if you have a basic understanding of HTML:
  "tags" define different levels of the structure, which in the case of MegaZine3 is related to a book logic:
  <book> as outer element (container) for <chapter> with <page> and then with content like <img>, <vid>, <snd>
  A basic overview can be found at
  http://www.megazine3.de/documentation.html Manuals and Introduction Guidelines
  
  Further downloads can be found on the download page:
  http://www.megazine3.de/downloads.html
  
  

MZ3 Online/Offline use

MegaZine3 runs on all computers with FLASH, i.e. almost all platforms but iPAD and iPhones.
Additionally MegaZine3 runs on Adobe's AIR framework. Which supports again Windows and OSx, but also Android, Blackberry and iOS (iPAD, iPhone

Summary

You can more (Windows) or less (MAC, Linux) comfortably create MegaZine3 titles on all systems.
You can run the final MZ3 titles/books on all systems with FLASH support, and additionally on iPADs, iPhones, Blackberries and Android systems with Adobe's free AIR framework.