Now that I have a handheld running Linux that's powerful enough to run Tcl/Tk comfortably, I've started moving my aqtools (formerly jstools) suite of Tk applications in PDA-ish directions. This consists of two things: (1) adding PIM applications (like a calendar), and (2) making sure the existing applications work smoothly on a PDA's tiny screen. The more interesting one is (2), since that involves rendering interfaces differently depending on what size screen you're on.
I hope to write a real calendar at some point, but so far I've got a really quick-and-dirty calendar along the lines of the old xcalendar that just keeps a file per day and lets you jot notes down for each day. If you're disciplined enough to type in event times, so much the better. :-) When run on the desktop, it can print PostScript month-on-a-page calendar pages.
I recently put together a pretty functional address-book application, and converted my address-book from the Agenda (which I'd previously converted from the Palm). Actually, it's a generic database manager (for little databases like addressbooks or CD catalogues), that comes with a config file that makes it work like an address-book.. I guess I should really do a new release of aqtools soon (and package it up for the iPAQ). :-) If you don't want to wait for that, feel free to send me mail and I'll give you what I've got now.
Above I called it a ‘Unix computer’, but that's not technically correct - little if any of the OS was strictly based on Unix source code derived from AT&T. The kernel was Mach, written at Carnegie Mellon University, and the commands and utilities were mostly from 4.3 BSD - largely rewritten from AT&T Unix, although there were probably some bits of AT&T code left. But on the command line, it felt like Unix.
It came, in the configuration I bought, with a 100Mb hard drive and 8Mb of RAM, for a total of 108Mb of storage. It had a 1152x864-pixel display with four shades of grey, for a total of 1,990,656 bits of display memory.
I have in my pocket as I write this in early 2002 another Unix computer, an iPAQ 3675 ‘Pocket PC’ running Linux (which I got in November of 2001. Again, it's not quite accurate to call it a Unix computer - it runs a kernel written (I believe) at the University of Helsinki, and the commands and utilities come from many sources, but are mostly rewrites from scratch by the GNU project. But on the command line, it feels like Unix.
The particular model I bought came with 32Mb of Flash ROM (rewritable non-volatile storage, somewhat comparable to a hard drive) and 64Mb of RAM, for a total of 96Mb of storage - pretty close to my NeXTstation. If it bothers me that that's not quite as much storage as my NeXTstation had, I can slide on an expansion sleeve and add a 128Mb Compact Flash card, for a total of more than twice the storage my NeXTstation had (when I bought it - I later got an external drive). It does come up short in the display arena, though - it has a 240x320-pixel screen with 4096 colours, for a total of 921,600 bits of display memory - a bit less than half that of the NeXTstation (and a much smaller screen, of course). It makes up for that by being able to go with me on the subway. And it's faster than my NeXT was.