Difference Between Zakat and Tax

Zakat and Tax are two completely different concepts.
Tax is collected from every person of a country or area by the government of the country or area.
If the person is rich he needs to pay tax and if he is poor even then he need to pay the tax on the items or things on which Tax is applied by the government.
Tax is forced by the government.
Tax is used for development of the country or particular area from where the Tax was collected. 

But Zakat is a different concept.
Zakat is applied on the people who can pay it.
There are some Nisab (rules) applied on the payer of Zakat.
If some body satisfies those Nisab (rules), he is eligible to pay the Zakat.
If somebody has 85 Grams Gold or 595 Grams Silver or if he has some currency equal to the above written quantity of Gold, he has to pay the Zakat on it.
Zakat is payable after one Lunar (moon) year if the above written quantity of gold, silver or money is kept by any person.
The Ratio of Zakat is 2.5% (Approx. 1/40). Zakat is used to help the poor people of the country or the area.
Zakat cannot be spent on the people who are not eligible for the Zakat.