The Articles of Confederation was the first constitution of the United States of America, describing the purpose and function of the federal government. The Articles were drafted by a committee appointed by the Second Continental Congress in June 1776, and the final draft was approved November 15, 1777 and sent to the states for ratification, a process that completed in March 1781. During this time, however, the Articles were the de facto system of government in use. Once ratified by all thirteen states, on March 1, 1781, Congress became the Congress of the Confederation.
The Articles established rules for the operation of the federal government, giving it the power to make war, engage in diplomacy, and handle issues in the western territories. Under the Articles, the states retained all powers not granted to the national government.
The representatives in the Second Continental Congress felt a need for a confederacy that would secure the independence of the United States while in the midst of the American War of Independence. However, Nationalists argued that the Articles were inadequate because they did not grant the federal government a taxing power, nor did they create executive or judicial powers. The Nationalists prevailed in the writing of the United States Constitution in 1787, and succeeded in gaining its ratification by 1788.
I highly recommend taking a few minutes to read the Articles and admire their simplicity. For more on why the Articles were so much better than the Constitution that (illegally) replaced them, see Scott Trask and Murray Rothbard (PDF, scroll to Chapter 45, page 253).
Under the Articles, the "President" was nothing more than a presiding officer. Just imagine: a government with no executive!