I'm looking for customizable content management system for company intranet application, Can SDL Tridion API (e.g. content-manager) be integrated with J2EE and running on the Apple OS X/Lion?
Well that really depends exactly what you mean. The SDL Tridion Content Delivery functionality (this is the presentation layer) is native Java. So yes, you can write just about any J2EE app you want to host a website which uses SDL Tridion published content. Further more, if you are using a newish version of Tridion (2011 or newer) you can also retieve content using the ODATA based web service.
If you are talking about working with the Content Manager (the place where editors work with content), the native API is written using Microsoft.NET, but you would most likley interact with the Core Service API which is web service based and accesible from Java.
Finally if you are just wondering if editors can work with content in the CMS, the Content Management Exploer and XPM both support modern browsers to edit content using OSX.
Welcome to the Tridion community.
Yes, Tridion is a very robust system and can be used to manage intranet and extranet content across various platforms/channels in multiple languages.
Tridion is a distributed architecture consisting of primarily of two sets of servers: 1) content manager and 2) content deliver/presentation.
Content Manager runs on a Windows Server environment, while Content Delivery can be almost any architecture you can imagine (but primarily the native Content Delivery APIs are Java, .Net or a RESTful web service (aka odata).
The Content Manager also has a web service API to manipulate items with the CM. This is known as the Core Service. So you may bind to it using clients based on any technology, including J2EE. Your custom app can of course be hosted anywhere you wish (e.g. Mac OS).
I highly recommend for you to read the documentation on SDL Live Content for a detailed explanation of the architecture and all the integration points. Here is the link (login required): http://sdllivecontent.sdl.com/LiveContent
It totally depends on what type and with what area you want to integrate. Following are the available integration points in SDL Tridion (you may search and learn for them in SDL Live Content):
1) Core Service - For interacting with Content Manager DB (e.g. related to CRUD operation in CMS)
2) Content Delivery API - For interacting with Broker DB (published data)
3) Storage Extension - For interacting with Storage Layer (you may want perform something in your J2EE application depending on storage activity in deployment)
4) Deployer Extension - For extending Deployer Process (you may want perform something in your J2EE application depending on your deployment process in Tridion)
5) Ambient Data Framework - For gathering and transforming website data
Below is the great article written by Bart on tackling integration in SDL Tridion, you may refer it for further details: Tackling Integration in SDL Tridion
Assuming your "infrastructure" consists only of Apple OS/X Lion machines then: No. SDL Tridion requires a windows system for the content management environment (published websites may be virtually anything). You would always need at least one Windows machine in your "infrastructure" to host the Tridion Content Management environment.