"There are thousand of treaties currently binding between two or more states, and also between states and international organizations, or between international organizations. Those thousands of treaties can be many different things. They can be about land or maritime border, trade, international aviation, the promotion and protection of investments, the protection of human rights, or the protection of the environment and biodiversity, the rule of war, judicial corporation between states and extradition, about disarmament, and so on." 

Examples of international treaties: United Nations, African Union, European Union, World Trade Organization, International Criminal Court, etc. 

There is a treaty on the law of treaties. It is called Vienna Convention on the Law of Treaties (1969), signed by 114 states and entered into force on January 27, 1980. Since it is called convention, it is applicable to states that not are partied to the treaty.