Is there any Sampler Groove/Rhythm machine or software/app having the following features:

1- Can load the audio loops/beats (e.g wav.) in different variations
(like A, B, C, D, 1, 2, 3 etc), which are switchable in real-time
when playing (on the fly) in perfect timing.

2- Can be MIDI synchronized with an external instrument midi clock as
a slave or master.

3- Can be able to change the tempo of audio loops/beats.

4- Have enough memory to store the audio (sample) loops.

Try Native Instruments Maschine https://www.native-instruments.com/en/products/maschine/

Thanks for your reply. Does NI Maschine switch or change the loop within tempo timing? I tried so many drum machines but most of them doesn't change the loop in tempo.

Should do, but best to try it out at your local dealer or contact Native Instruments to make sure, but pretty much everything has time stretch and pitch shift these days, (The only way to alter audio files) plus most will accept or can create REX files which enables you to control t like Midi. (Maschine tends to be the go to product for versatility)

Bill