When comparing Signal vs Zulip, the Slant community recommends Zulip for most people. In the question“What is the best chat software?” Zulip is ranked 11th while Signal is ranked 13th. The most important reason people chose Zulip is:
Instead of rooms or channels Zulip is built around topics. This allows you to have multiple conversations at the same time without conversations interfering with each another. It also allows you to reference conversations without clutter.
Specs
Question Ranking
Pros
Pro Provides security and privacy
Signal uses an advanced end to end encryption protocol that provides privacy for every message every time.
Pro Free and open source
Signal is free and open source software, enabling anyone to verify its security by auditing the code. It's the only private messenger that uses open source, peer-reviewed cryptographic protocols to keep your messages safe.
Pro SMS/MMS support
Signal can be your default SMS/MMS text messenger. Encryption is not possible when sending SMS to your contacts, however.
Pro Recommended by Edward Snowden
Edward Snowden uses this messenger and recommends it to everony who is concerned about his privacy.
Pro Supports sharing of various different media types
Signal supports: emoji, pictures, videos, audio, contacts, any location and GIF.
Pro Supports encrypted group chats
Pro Message mirroring on Signal Desktop
Signal Desktop is a Chrome extension that allows you to mirror messages from your phone, including replying.
Pro You can easily view all media exchanged
You can easily view all media shared in the chat without scrolling back to when it was shared.
Pro Helps keep track of different conversations
Instead of rooms or channels Zulip is built around topics. This allows you to have multiple conversations at the same time without conversations interfering with each another. It also allows you to reference conversations without clutter.
Pro Easy asynchronous conversations
Its threaded model helps people working in different timezone's communicate effectively.
Cons
Con Needs access to your phone number and contacts to work
Con If SMS/MMS imported, other apps can't read SMS
For those using Join, Pushbullet, or similar apps to send and receive SMS/MMS from web or desktop, putting your SMS in Signal somehow breaks this functionally. The dev is aware but plans to remedy the situation have not been named a priority
Con Single device
Signal can only be registered to one mobile device at a time. But you can link Signal to Signal Desktop.
Con Uses message mirroring
You phone must be on and connected to the internet for Signal Desktop to work.
Con Takes some getting used to
As most chat software uses the concept of channels or rooms, getting in the habit of splitting each topic off in a separate category can require some getting used to and discipline.