Kaleidoscope 2.3.1 is a maintenance release, addressing problems with the menu bar clock under Mac OS 9.1, extended menu borders under Mac OS 8.1, and potential crashes when printing. It also fixes conflicts with AliasMenu, MYOB AccountEdge, ColorSwitch Pro, Style, Macromedia Fireworks, BBEdit, and Microsoft Office 2001.
Kaleidoscope overhauls your Macis user interface using plug-in files called "schemes". Kaleidoscope comes with several schemes by interface designer Arlo Rose, formerly of Appleis Human Interface Design Center, and there are thousands more third party schemes available from the Kaleidoscope Scheme Archive (KSA).
Kaleidoscope is available for US$20 (shareware) and you can find more information about it at Kaileidoscope.net.