The best free alternative to Cortana is Mycroft, which is also Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to Cortana and many of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to Cortana are Google Assistant, Siri, Braina and Siri Shortcuts.
Siri Shortcuts deliver a quick way to get things done with your apps with just a tap or by asking Siri. The Shortcuts app enables you to create personal shortcuts with multiple steps from your favorite apps.
Control applications or games by voice commands and/or by the press of a keyboard, mouse button or combinations of it, additionaly you can start any of your macros by scheduler, by a macro action, or from an external program.