I love using touch with Windows 7 and 8. Especially on Windows 8, the touchscreen finally feels like it's respected just as much as the keyboard and mouse.
So, naturally, I'd want to carry this experience over to the Mac. I've used a Macbook/MBP trackpad, but those aren't the same. They are not nearly as large and usable as a full touchscreen.
So: Does the Mac support touch screens in any way?
One way to get something close, is to use your iPad as a secondary display to your Mac. In this way you are able to extend your normal desktop onto the iPad and input using touch.
Update (2017-03-05): Since Yosemite (10.10), T232HL seems to be far less buggy. However, it's still not very multi-touch.
23" Acer T232HL works without issues with Windows 8.x and Ubuntu 14.04 -- but not with the latest-and-greatest stable release, OS X Mavericks.
OS X Mavericks recognizes it, but first few touches always go to upper-left corner (coordinates 0,0) and are interpreted as a click. Only third or fourth touch goes to the proper place -- but at that time it's already in the "click" phase, so the touch gets interpreted as a drag. It also gets recognized as a graphics tablet (Ink icon appears in System Preferences), but other than that, touchscreen is fairly useless with OS X.
Which is a shame, as its usefulness would be a middle ground between usability under Windows and Linux.
All this happens with a monitor that, to the best of my knowledge, represents itself as a standard USB HID device.
Hence, despite what other answers claim, I'd say multitouch screen support on OS X is incomplete and broken. Drawing conclusions based on multitouch touchpads or singletouch screens or singletouch graphics tablets is silly and incorrect.
There are some third-party commercial drivers that perform some magic to get multitouch screens into a usable state. Since the question was presumably about the stock OS, discussing them is out of scope for this answer.
Touch-Base offers drivers for multi-touch support with their software UPDD Touch. According to their website, version 6 supports macOS 10.8 and above:
Our drivers can be used to add touch support where none exist or for enhanced functionality not offered by the native driver support or to support touch hardware not supported in certain operating system releases. UPDD supports multi-touch at an operating system level (if supported) but also at a native UPDD API and TUIO Server level allowing for the development and support of multi-touch and multi-user UPDD API and TUIO client applications.
...
UPDD V6 driver is available for MacOS 10.8 and above. It supports legacy serial and non-HID USB devices as well as modern HID USB devices. When using a multi-touch touch screen it supports full multi-touch gestures, mimicking the functionality of a multi-touch trackpad or magic mouse. UPDD V5 is still available for Mac OS X 10.6 and 10.7.
UPDD Touch Software is not cheap though: a single MacOS and Windows commercial / business license is USD 150, EUR 120, GBP 95.
Check the documentation for more information.
As far as I know, there is currently no native support for touch screens on OS X. I strongly believe this is because Apple wants you to do that on iOS instead, so I don't see touch adoption on OS X in the near future.
