Macro Deck - Use smartphone as macropad for pc
Remote Mouse - Turn your smartphone into a wireless touchpad and keyboard now!
TouchPortal - Touch Portal is a companion app to control a PC or a Mac by using a deck of buttons to improve the workflow & productivity of game streamers, content creators and professionals.
KDE Connect - Integrate Android with the KDE Desktop
Deckboard - Deckboard helps you create macros for Windows PC and launch them on your phone.
LEA Extended Input - iOS/Android app with windows server to control functions in games via your smartphone/tablet.