Term2 is a replacement for Terminal and the successor to iTerm. It works on Macs with Leopard or Snow Leopard.
Divide a tab up into multiple panes, each one of which shows a different session. You can slice vertically and horizontally and create any number of panes in any imaginable arrangement.
Map any key to any function. Assign separate functions to each option key--or even remap all the modifier keys. You can customize iTerm2's appearance to suit your needs: enable transparency, background blur, background images, and much more.