Tcl/Tk is very mature, has a small footprint, is easy to learn and use, and uses native widgets on Windows and the Mac. Plus, it has a deployment mechanism second to none by way of starpacks, starkits and tclkits. You can either create a single-file executable (starpack) that embeds a very full featured virtual filesystem, or a two-file solution of a platform-specific runtime engine (tclkit) with a platform-independent application file (starkit).
It s downside is that it s low on "flash" -- there s not a lot of support for transparency, multimedia, animation and fancy graphics. So, depending on whether or not you need a lot of eye candy it may or may not be the right choice for you.