black-hole is a configurable XMPP ↔ Discord bridge written in Python 3.6.
It uses Discord.py@rewrite and aioxmpp.
Worth reading through just because it demonstrates how to use aioxmpp.
Ripcord is a desktop chat client for group-centric services like Slack and Discord. It provides a traditional compact desktop interface designed for power users. It's not built on top of web browser technology: it responds quickly to input, sips gently from computer resources, and gets out of your way. It does voice chat, too.
Number one feature: "Not made from a web browser."
A universal bridge for communications protocols. Presents a unified REST API so you don't have to worry about writing your own protocol adapters.
Protocols: IRC, XMPP, Gitter, Mattermost, Slack, Discord, Telegram, Rocket.Chat, Hipchat (via XMPP), Matrix, Steam, ssh-chat and Zulip
Appears that it's "one instance of this bridge to one service at a time."