KDE Connect - Integrate Android with the KDE Desktop
Typeeto - Use Mac’s keyboard to type on iPad, iPhone, Android, etc.
Synergy - Cross-platform software for sharing your mouse and keyboard between multiple computers
Type2phone - Type2Phone: Use your Mac as keyboard for iOS devices
AirMore - AirMore is a cross-platform toolset that can help you manage any Android device wirelessly.
1keyboard - Type on your iPhone, iPad or AppleTV using your Mac keyboard