Alerting in Kibana

Hi all, i saw alerting is paid version like sending mail or slack. I saw there is alterntive which iselastalert2. However, there is elastalert as well .what the difference. I plan to use docker

elastalert & elastalert2 are different.
There is one more variation available with praeco; which provides web ui.

i her elastalert2 extends elasalert. but no proper documentation to show the difference. which is the best