OnTopReplica is not available for Mac but there are some alternatives that runs on macOS with similar functionality. The best Mac alternative is Helium, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to OnTopReplica and six of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to OnTopReplica are Pennywise (Free, Open Source), PiP for Mac (Free, Open Source), Afloat (Free, Open Source) and Picture In Picture (Paid).
Pennywise opens any website or media in a small floating window that remains on top of all other applications. Pennywise windows stays up all the time. No need to keep struggling with alt + tab, use Pennywise for easy multitasking.
Clone any visibile window Crop the preview Auto and manual resize preserving the aspect ratio Multiple window preview from same process, cmd+n to open and cmd+w to close Pinch to zoom Click-through Opacity control
Keep windows afloat (heh) on top of all others. Pin windows to the desktop. Move windows from anywhere, not just the title bar. Turn a window into an "overlay" on your screen that doesn't hinder your work.
Picture in Picture (PiP) allows watching videos from the internet while working at a computer. Using unique algorithms, the program finds videos on web pages and allows to open them in a floating window, that remains in the front.
Duplicate Windows visually copies any window in Mac OS X live and on-the-fly. It’s like display mirroring for individual windows! I created the tool to display windows across multiple monitors in extended desktop mode during presentations.