Web sphere is an IDE. Can it act as a web server or application server ?What does server do that web sphere does not ? It can develop an application, I can access that application from other computer. (or websphere does not have web server ?). Web logic is following j2ee standards like websphere, so whats the difference between weblogic and websphere?
WebSphere and WebLogic both provide application servers that comply to the J2EE standard. Just like Toyota and Ford create cars that comply to Highway Safety standards. You can deploy J2EE applications to both servers.
But they compete on scalability, robustness, ease of integration, extra features, price, reliability, and any other point you want to compete on. And there are many vendors in the J2EE space, not just WebSphere and WebLogic, although I do believe they are the two biggest players.