I have 2 such devices, both Cassiopedias (E-100 and E-105) and really have seen no need to upgrade them. They work just great for how I use them (note taking, outlining, sketching/painting "on the go") plus they have bright, big (3.75") displays. Too bad Casio abandoned them. They got it right the first time out of the gate! Amazing.
I use the following software on both of them (albeit older versions you
WILL have to hunt down).Conduits TaskSwitcher 1.1
Old version, puts a button (with bmp of your choice) into the Windows logo of your start bar and enables gestures & clicks over the button to start/stop/switch between running apps. Pure simplicity. Essential.
Also at that site (Conduits): PocketArtist (I'm on v1.1) and PocketPlayer (1.21). Pocket Artist
IMHO is the best of the painter programs, well designed for small screen and stylus. PocketPlayer
is great for MP3s.TotalCommander Pocket 2.5 beta (freeware)
Total Commander in your PPC. Dual file panels, zip/unzip, custom buttons, drag and drop to toolbar, favorites, history. Indispensible.ListPro 2.0
Best hierarchical notetaker/list manager out there. Multiple lists, custom fields, hierarchical (ie. outline) data types, etc. PC Synch. Main man.BugMe! 3.1
Combined sketching, text notes from the PPC tray. This is the old B&W version. The latest (color) version is not so useful. Great for quick jots.StarTap
Kitchen sink. Hard to describe. Taskbar utilities, quicklaunch panels, etc. etc. Good bitmap viewer that I use with TotalCommander Pocket.
Also (can't find websites for these!):
FootPrint Software PS/PC Outliner (Beta 2, 1998!!!)
A full featured outlining tool. Works a treat.
Excel compatible spreadsheet with tabbed interface. No "About" box no info about it in the software. Used it for years.
A simple utility to turn off the PPC with a single tap.
My Casios are perfect for my purposes. Sort of wish sometimes I could justify a newer machine. It'd be faster and have more features, but the screen would be smaller and there would be no enhancement over the function I already have. Both my units still work perfectly. I found batteries on eBay.