No, you’re probably thinking of Rift, which is a fork of Glide.
OmniWM itself was written from scratch, which you can see in both the Git history and the current codebase. Glide was never used as a codebase or foundation for OmniWM. Before starting OmniWM, I explored several existing macOS window managers, including Aerospace, Rift, Glide, and BobrWM, because I was looking for something that could support everything I had in mind. Ultimately, none of them provided the foundation I needed, so I started OmniWM from scratch.
That said, I absolutely want to give credit where it is due. PaperWM.spoon was, as far as I know, the first real animated scrolling window manager on macOS. The first Niri-like layout work I was involved with on macOS was in Glide through my PR, with a lot of help from Tmandry, who is an incredibly knowledgeable and professional developer 🫡
OmniWM is where I eventually took the idea much further and built what I consider a full Niri-style scrolling layout for macOS, alongside the other layouts and functionality I wanted OmniWM to have.
So Glide and tmandry’s work were definitely part of the journey and deserve credit, but Glide was not the basis or codebase of OmniWM.
And on that note, I would genuinely love to see Tmandry join OmniWM someday. I think we could achieve some pretty incredible things working together, especially with how much Swift itself has evolved. Swift now has a powerful ownership model with borrowing, consuming, noncopyable types, and related features that bring some of the same ideas that make Rust so attractive for systems programming into Swift, while still retaining first class access to the macOS ecosystem. I think there is a lot of unexplored potential there for a native macOS window manager, and having someone with his knowledge and experience involved would only push it further.