Difficult to put an exact figure on the number of software titles compatible with OS X. It will probably run into the millions. Most of the major software developers (such as Microsoft and Adobe) have their own Mac developers working on Mac software. Then there are countless smaller developers producing software for Mac OS X. (See links below for an idea of the range)
IrfanView is free software that is compatible with OS products. You can download this software for free online from websites such as Cnet and FileHippo.
No
The operating systems that are compatible with Adobe software include Windows 7, Windows 8, Mac OS X, Mac OS X Snow Leopard and Mac OS X Mountain Lion.
Omnigaffle is a charting software, similar to Microsoft Visio. Omnigaffle is compatible with Apple devices: Mac OS X Leopard, Mac OS X Snow Leopard, Mac OS X Lion and iOS (iPad).
Both Apple and IBM are large international companies offering a wide range of software and hardware. IBM has a range of software for Mac OS X such as their Lotus Symphony but they have discontinued other titles such as their XL C/C++ Compiler Advanced Edition for Mac OS X.
Yes OS X supports P2P protocols and many other common protocols to windows, so there should not be a problem as long as you have compatible software.
There are several emulators to run other systems software on Windows, but there is nothing decent (as in working reliably with any software) for running Mac OS X software on Windows.
The current version of Airport Utility 5.4.2 and it is fully compatible with Mac OS X 10.6 (Snow Leopard). The latest versions of all Apple software can be installed by selecting Software Update... from the Apple menu.
Infortunetely Apple wrote the software when they made 10.5 and did not make it backwards compatible.
The latest BlackBerry software currently on the market is the "BlackBerry 10 OS" according to the company's website. However, this software is not compatible with BlackBerry phones using BlackBerry 7 OS and earlier. BlackBerry 10 OS is an all-new BlackBerry experience, and is not available as an update to older phones.
Yes, the Elgato Game Capture HD comes with its own software for Mac OS X 10.7 or higher.
To use a Logitech (or many other USB)) webcaminstall the Macam software which will enable the use of the webcam with Mac OS X. (See links below)