I mean succeeded in replicating it, not necessarily as a business.

It doesn't seem so. I tested all I could find, LiteTracker seems the best, but still extremely buggy even in the initial demo project changing task status fails. The rest appears either half-finished, untrustworthy or has a very sketchy interface. But would really like to be surprised.

I am very rarely willing to pay for software and this is one case I really want to, but cannot find anything.

This thing kinda feeds my pet theory that the art of making functional software has been lost by late 2010s. People say Linear is fast but it's nothing compared to how well Pivotal worked. Any half-skilled indie dev could have made a killing on making a good replacement, but no one has been able to?