Navid Shafie said about 4 years ago on puma-dev replacement for pow and prax :
[SOLVED] For future reference for others if they had same issue as me. My problem was that I had programs running on port 80, so I ran ** lsof -t -i :80** and saw the programs running there, after that I ran ** lsof -t -i :81** (or **lsof -t -i :YOUR-PORT**) to check if anything running there and it wasn't so I did **puma-dev -install -install-port 81** and that solved my issue. Another issue some Mac (chrome) user can face is the certificate issue. What I did was to drag the certificate to my desktop and than drag it to my keychain and allow everything, quite and restart chrome and my problem was solved. Thanks for great series @kobaltz