gifSlap is described as 'Gifs as Footage: No more converting videos between codecs. Point gifSlap to your gifs folder and get started. Control Options: Use a MIDI controller, keyboard and mouse, or even a USB Gamepad. Made for Performing: Patterns are generated in real time on a separate window' and is an app in the Audio & Music category. There are five alternatives to gifSlap for Mac, Windows and Linux. The best alternative is Pure Data, which is both free and Open Source. Other great apps like gifSlap are Max/MSP (Paid), ORCA (Free, Open Source), VDMX (Paid) and PraxisLIVE (Free, Open Source).
Pd (aka Pure Data) is a real-time graphical programming environment for audio, video, and graphical processing. It is the third major branch of the family of patcher programming languages known as Max (Max/FTS, ISPW Max, Max/MSP, jMax, etc.
Orca is an Esoteric Programming Language and live-coding environment for musical experimentation. In Orca, each letter of the alphabet is an operation, lowercase letters operate on bang, uppercase letters operate each frame.
VDMX5 was created from the ground up to meet the demands of realtime video performance. Built around a robust data processing architecture it was designed to be used with whatever hardware- or software- you've got available.