Caster

Osprey is an application while Caster is a collection of scripts that are loaded through Dragonfly
Caster uses the Dragonfly API whereas Osprey provides its own simplified API that is built on top of Dragonfly
Osprey supports displaying the transcripts as desktop notifications
Osprey has an applet
Osprey is much more modular with its configurations
- no configurations are included by default (though it is recommended to use the osprey-starter-pack)
- configurations are enabled by adding them to the Osprey config directory

Talon

Context.keymap changed to Context.set_commands
Context.list changed to Context.set_choices and it now takes a dict of lists instead of just one list
Specifying a list in a rule has changed from {context.list} to <list>
Str has been changed to insert and it's now just a regular function instead of creating and returning a callback
Rep has been changed to repeat and it's now just a regular function instead of creating and returning a callback
press has been changed so that the key separator is now ' ' instead of '-'
The default ContextGroup has been renamed from talon to default_context_group
ContextGroups are now loaded automatically so you don't need to call ContextGroup.load()
<dgnwords> has been replaced with <word>
<dgndictation> and its variations has been replaced with <phrase>
Some of the keys have been changed. Check out the API documentation for the specifics.