What is the difference between Salesforce System.Assert and System.AssertEquals?

System.Assert accepts two parameters, one (mandatory) which is the condition to test for and the other a message (optional) to display should that condition be false.
System.AssertEquals and System.AssertNotEquals both accept three parameters; the first two (mandatory) are the variables that will be tested for in/equality and the third (optional) is the message to display if the assert results in false.