According to users of the WristPDA mailing list, Fossil has recently taken the SDK for its PalmOS-based watch off line. In case anyone wants to download the WristPDA SDK, you can get it here(cached on tamoggemon.com):
As for creating new applications for the WPDA(being completely honest) – I can not recommend this to anyone wanting to make money off his programs. The amount of active WristPDA users is getting smaller day by day; there are next to no sales anymore. On the other hand, if you just want a specific app to run on the WPDA(and get it running), please send us a press sample so that it can be reviewed.
P.s. Here’s a bit of further reading while the SDK is being downloaded: