Mattermost is popular in Eclipse community and therefore all eclipse projects channels are hosted in https://mattermost.eclipse.org
Go to the link and create your own account. After login, search the public channel with keyword ‘kiso’, you will find us, then welcome home.
You can also access it via the logo on the top right of the page.
Another way to reach us is still the old-school mailing list, which is email@example.com.