IRC is such a simple protocol seeing its implementation in <1k loc in many languages and I assume bot building process must be simple too compared to signal.

I have built bare minimum hello world bots in simplex and session and I think both had a lot of troubles to go through but if someone's interested, they can look at simplex for bot creation but they started to have client side verification/alert of content which admittedly is a very honeypot-alike activity/slippery slope itself.

Signal has some of the least controversies even though its centralized, Matrix is another good one and personally I sort of prefer matrix because all these other protocols require apps whereas matrix can work on top of a browser thus having more widespread adoption imo.

XMPP is another good protocol and at this point pardon me for yapping but I once saw someone break a nat using XMPP and using it to create website endpoint creation which was good too but personally I feel like signal is the most trustworthy overall. I wish someone can make signal's bot genuinely simple as telegram bot creation as there is a lot of potential