First things first: A.D. does not stand for "After Death". It's an abbreviation of the Latin "Anno Domini" or "The Year of Our Lord". So it begins with the birth of Jesus, not the death. Otherwise you'd have this ~30 year gap between the end of one system and the beginning of the next, while he was alive.

Secondly, there are many systems, but they basically all start counting from some significant date, just like A.D. does. A lot of monarchies will count from the start of a king or queen's reign, so "In the fifth year of the reign of Ramses II". This continued long after the AD system was introduced, and often used in parallel. I believe England/Britain kept using regnal years into the 20th century on paperwork, along with AD. In some places, it's still the appropriate way to talk about the year. This is the 64th year of the reign of Elizabeth II. Rome had two sorts of systems, one that counted "Ab Urbe Condita", or "From the Founding of the City" (which was probably mythical, and we don't actually know when Rome was founded) and one that named the year by who the Consuls were. This meant that say, 42 BC is The Year of the Consuls Lepidus and Plancus. In 59 BC, Julius Caesar had so much power and his colleague was routinely ignored, so people jokingly called it "The Year of Julius and Caesar".

There are still other calendar systems, like the Maya calendar that has two different calculations of years, one that lasts 365 days, and one that lasts 260 days. They match up every 52 years for a "calendar round". During the French Revolution, they tried a new calendar with 10 days in a week, and new names for everything, that started counting in 1792. It was used for 12 years (and then briefly again during the Paris Commune.

There are many other types of calendar, but these are some of the most common and most notable.