Haskell has been around for more than a decade and had huge uptake by language nerds, but the only significant OSS written in it is Pandoc. In contrast, Rust already has Servo and a number of CLI tools, ripgrep being the most prominent.
I'm not sure what you consider 'significant', but to my mind, there are many great haskell open source projects: xmonad, shellcheck, stack, haxl, to name a few.
Not to mention how many languages are written in it: Elm, Purescript, Idris, GHC itself.
