Sometimes, you can find multiple versions of a specific work because they are no longer under copyright. Works that were published before current copyright laws are said to be in the public domain. Othello and Oedipus are both in the public domain, and all of the below links will provide you with the full text of the works in different formats.
In contrast, you can see that A Raisin in the Sun is still under copyright, which is why there are fewer options to read the play.
Sample MLA Citation
Hurston, Zora Neale. "Sweat." The Complete Stories. 1st ed. New York: Harper Collins, 1995. 73-85. Print.