screensy is described as 'Screensy is a simple peer-to-peer screen sharing solution' and is an app in the File Sharing category. There are more than 100 alternatives to screensy for a variety of platforms, including Windows, Mac, Linux, Android and iPhone. The best alternative is TeamViewer. It's not free, so if you're looking for a free alternative, you could try Chrome Remote Desktop or Remmina. Other great apps like screensy are AnyDesk (Free Personal), DWService (Freemium), Parsec (Freemium) and UltraVNC (Free, Open Source).
Remmina is a remote desktop client written in GTK+. Remmina primarily targets system administrators and travelers that need to work with computers remotely in front of either large monitors or tiny netbooks.
DWService is an half (only the client/agent) open source project which offers a service that allows access to remote systems (Windows, Mac, Linux, Raspberry...) using a standard web browser - without any component required on the client side.
UltraVNC is easy to use and free software that can display the screen of another computer (via the Internet or a local network) on your own screen. The program allows you to use your mouse and keyboard to control the other computer remotely.
TightVNC is a free remote desktop application. With TightVNC, you can see the desktop of a remote machine and control it with your local mouse and keyboard, just like you would do it sitting in the front of that computer.
VNC is remote access and control software which allows you to view and fully interact with one computer desktop (the "VNC Connect") using a simple program (the "VNC viewer") on another computer desktop or mobile device anywhere on the Internet.