HanDBase: Extremely powerful PalmPilot database program supporting up to 30 databases, 30 fields each, many field types, extensive sorting, filtering, and searching options.
JFile Pro: The first full featured database program for the PalmPilot. Supports up to 30 databases with 50 fields each, many field types, multiple sorting and filtering options.
List: Database program for the PalmPilot. Supports up to 12 databases, 3 fields per database, simple sorting. Freeware. Source available.
MobileDB: Palm database software from Mobile Generation Software. Supports up to 20 databases with 20 fields each, multiple sorting and filtering options.
MobileDB Lite: Supports MobileDB databases as read-only; you cannot modify the databases and you cannot create new ones. Freeware.
Palm OS Database Comparison Review: Excellent review of the available database software for the PalmPilot.