I am an Australian. Australian English is unique. (The greatest similarity is with New Zealand English, however there are also differences here too, minor differences, although some may have difficulties differentiating.) In comparison to the “main stream” English versions; British and American English, Australian English generally is generally closer to the British English, however popular culture and the large influx of American media in the past 50 or so years means it is reasonably flexible.
Australia is basically metric, following the ISO metric system (AS ISO 1000), although some of the basic archaic units are still commonly used, but particularly (and strangely) for baby weights. Some people still talk about weights using the Stone unit (British). Inch, feet, pound, etc. units are still used, but this seems to be slowly fading away with time. Australia officially and effectively went metric in the 1970's.
Australian's are generally taught to spell using British English, but are flexible with American English: colour/color, systemise/systemize, etc., but tend to use the British version formally.
Australians generally use the standard US keyboard, we have AU$, and do not use £ (pound currency), so the British keyboard is not normally used or preferred. (The British keyboard mapping is generally a pain in the arse for us, when it is somehow default mapped!) (The Australian dollar replace the Australian pound in 1966.)
I recently was reminded that American's call the # symbol “pound”, whereas we call it a “hash”. A Logical exception is when referencing American standards, eg. ANSI B16.5 Class 150# flange.
Australia (see AS1612, ISO216 and ISO217) uses the ISO A paper sizes, mostly A4(210x297mm) and A3(297x420mm). We like most of the rest of the world, outside the North America, use ISO A sizes. The American(US) software that tends to hard default to LETTER size is a pain in the arse. (Microsoft). Sadly many neophytes (idiots) in Australia do not know (or care) about this issue and use the default American software setting, so documents are often in LETTER size or perhaps worse, a Amish-mash or LETTER and A4! Modern printers often auto scale between A4 and LETTER size, shrinking the page contents about 8%.
Australia follows the general English speaking convention for use of Decimal marks in numbers, that is, decimal points not decimal commas.
Date and time formats. Australia tends to culturally follow the British (and Europeans) in this, day/month/year and hours:minutes:seconds(AM/PM). The Australian Standard AS ISO 8601, “Data elements and interchange formats - Information interchange - Representation of dates and times” and is identical to ISO 8601:2004. (The ISO 8601 date format is the most logical and follows the standard number format of most to least significant. The pervasive US date format using Month/Day/Year, is the least logical, mixing number significance!) (I prefer the ISO version of date and time YY-MM-DD HH:MM:SS.)
Time zones, Australia is mainly spread across 3 time zones, which is further complicated by daylight savings in the southern eastern states. The east coast is nominally +10UTC and the west coast is +8UTC. I do not like daylight savings and am fortunate to live in a place that does not use it (Western Australia). Daylight savings makes no sense in localities that are close to the equator (close to and within the tropics), as the variation of day lengths throughout the year is minimal.
Interestingly, although Western Australia's population is relatively low, circa 3 million people, it is is in the most populous world time zone, as it includes: China, Taiwan, Philippines, Indonesia (part), Malaysia, eastern Russia (part) and within a +/-1hour timezone all of Indonesia, Vietnam, Thailand, Burma, Cambodia, Laos, Mongolia, Japan, Korea, Singapore and more of Eastern Russia.