Ask HN: Decent, secure IM app that works on iOS and OS X?

Your best bet is to use OTR encryption over XMPP or another messaging protocol of your choosing. Also configure clients to use SSL/TLS.

You can learn more about OTR here: https://en.wikipedia.org/wiki/Off-the-Record_Messaging

You will actually be using a different client on your iOS devices compared to OSX. Just use the same account/protocol and you will be fine. On MacOS you will probably want to use Adium. On iOS use ChatSecure.

Sweet will give ChatSecure a try.

What about a Jabber client?

ChatSecure and Monal are both excellent Jabber iOS clients that support encryption with Adium on the desktop? You can run you own Jabber server (ejabberd) or use one of the free ones out there (DuckDuckGo, https://xmpp.net/directory.php). It's not as nice as Telegram or iMessage but it works.

I'm using Telegram too. Works fine for me.

I don't follow.

What is your issue with Telegram? How is Telegram iMessage?