Original Clever lists by André Luís

.ori li { float:left; margin: 0;outline: 1px solid black}
.ori li:nth-child(1):nth-last-child(1) { width: 100%;}
.ori li:nth-child(1):nth-last-child(2), .ori li:nth-child(2):nth-last-child(1) { width: 50%;}
.ori li:nth-child(1):nth-last-child(3), .ori li:nth-child(2):nth-last-child(2), .ori li:nth-child(3):nth-last-child(1) { width: 33.33%;}
.ori li { background-color: red; color: white; list-style:none; }

first example

ul.first { float:left; width:100%; cleat: both }
.first li { background: green; color:white; outline: 1px solid black; float:left; width:33.33% }
.first li:only-child{ width:100%}
.first li:nth-child(1):nth-last-child(2),.first li:nth-child(2):nth-last-child(1) { width: 50%;}

second example

ul.second { display:table; width:100%}
.second li { background: brown; color: white; border: 1px solid white; }
.second li { display: table-cell; width:auto }