[ZenoArrow]

Ruby is dominated by Rails, but Rails sidesteps the issues of undefined state by 'convention over configuration'.

As for other Ruby projects, static typing would help with performance issues, why developers choose not to add types when hitting performance bottlenecks is not something I fully understand, perhaps it's just seen as normal to rely on C modules to increase performance. That said, Graal/Truffle does seem to offer hope that Ruby performance can be greatly improved.