What are the replaceable rules?
The Corporations Act 2001 provides a number of "replaceable rules", mainly for companies that do not have a constitution (although they can also apply to a company if the company's constitution does not exclude them). The replaceable rules basically provide for the terms of the relationship between the directors, the members (shareholders), and the company, and can be found throughout the Corporations Act 2001 (S.141 of the Corporations Act 2001 provides a table of replaceable rules found in that Act).
It should be noted that they do not apply to a proprietary company while the same person is both its sole director and sole shareholder (refer S.135(1) of the Corporations Act 2001). See S.198E, S.201F and S.202C for the special provisions that apply to a proprietary company while the same person is both its sole director and sole shareholder.