Could I use MODx to do this ?

I want to create an internaml web site with a PHP Framework
This framework need to the hability mostly to
* monitor system activity using php scripts already tested which generate an array
* allow to create an spreadsheet from array
* get file and content with ftp

The monitoring could be consider as a post with two parts:
one part automatically generated by a php script after filling a formula (name of the system)
and the second part manually entered by the user.
I don’t know yet if MODx fullfills those requirements, can integrate Pear modules like spreadsheet_excel, net_ftp ...

Everything you want is not really revelant concerning MODx abilities.

What should matter is do you need a "content management system" to second your own script?

As a matter of fact, i did use PEAR in conjunction with MODx, and as a lot of people here, i did also use my own scripts for very different scenario.

So basically you can integratealmost any-php script with MODx, it just depend on your integration requirements and your PHP knowledge.