I have been looking for tools which allows you to create cross platform applications as well as be able to host the same application on the Web.
I came across XAMPP which run on Linux, Mac, Windows and even Solaris!
Its a bundle of Apache, MySQL, PHP/Perl and other goodies to all these platforms. If you can do with Web based apps this would work. You can always use AJAX if you need more rich client experience.
This can be used to host applications which can be developed in PHP or Perl.
A big advantage of this is that you can use several of open source applications written for the LAMP stack such as Media Wiki, Drupal, etc. which can be used for creating intranets.
Disadvantage would be that this may not as portable as Java or Mono.
Check it out. – XAMPP.