How is social justice achieved in Islam; is it through Zakat alone, or through other means as well?

The Islamic Sharia is valid for all times and places, and it achieves progress and security for the individual and society through its rulings and directives that build a cooperative and interdependent society. This interdependence is achieved through:

1. Zakat: An important source of aid for the poor and the needy. 2. Expiations (Kaffarat): A source of livelihood for the poor and the needy. 3. Spoils of War (Ghanima) and Fay’ (booty taken without fighting): The poor and needy have a share in it, as Allah Almighty says: (And know that whatever you take as spoils of war – then indeed, for Allah is one fifth of it and for the Messenger and for [his] near relatives and the orphans, the needy, and the traveler) [Al-Anfal:41], and His saying: (What Allah has granted His Messenger as spoils from the people of the towns – it is for Allah and for the Messenger and for [his] near relatives and orphans and the [stranded] traveler – so that it will not be a perpetual distribution among the rich among you) [Al-Hashr:7]. 4. Caring for the widow and sponsoring the orphan. 5. Maintaining kinship ties. 6. Kindness to neighbors, honoring guests, and helping those in need. 7. Enjoining good and forbidding evil, and offering sincere advice. 8. Manners that achieve harmony, such as greeting with peace (salam), seeking permission, lowering the gaze, and respecting elders. 9. Filial piety towards parents and caring for them, and advising on the upbringing of sons and daughters. 10. The obligation of the tribe and clan to stand with the individual during crises, such as accidental killing. 11. If the previous provisions fail, a Muslim is forbidden from withholding from his brother the surplus he needs to save himself or his property.

Sharia includes many forms to achieve social justice.