this webpage needs an update: http://zmugvt6onw4mpu5w.onion/infra/otr-im-website/blob/master/clients.html
the app "TextSecure" was renamed to "Signal" and is also aviable cross plattform. your may update the weblink to: https://whispersystems.org
also, "We would like to thank Gandi for providing us with a wildcard SSL certificate." in the bottom of the page seems expired when your now using Letsencryypt.