Why we can send email from proton to gmail but cannot send message from whatsapp to signal?
I think Proton could come with federated, decentralized communication solution, which use Signal protocol and allows users to comunicate from Singal to Proton, from Proton to Telegram, iMessage or any other messangers.

The idea of a Proton messaging app is appealing—combining end-to-end encryption with SMS/RCS support and integration with Proton’s ecosystem could create a unified, privacy-focused communication platform. It could leverage Proton’s reputation for security while giving users a convenient way to message contacts who aren’t on encrypted networks.

However, building such an app is challenging. Signal already provides trusted, robust encrypted messaging, so a new app risks redundancy. Adoption is crucial—messaging apps only work if your contacts use them. Supporting multiple platforms, bridging to SMS/RCS, and potentially federated protocols adds technical complexity and privacy trade-offs. Maintaining this long-term would require significant resources.

For a Proton Messenger to succeed, it would need strong encryption, user-friendly features, seamless compatibility, and a clear advantage over existing solutions. Otherwise, it risks being “just another messenger” with limited adoption.

In short, it’s a promising idea that fits Proton’s privacy ethos, but executing it well would be difficult.
https://medium.com/@albertmofficial/smart-home-revolution-blending-technology-with-timeless-design-02f10047df4c

SimpleX did it already.

I think it would make sense. Just partner with Threema ;)

Proton should be email only IMO. Living in ecosystems is a trap. Decentralize as much as possible. Never put your eggs in one basket.

it's not about the app, it's about how many people use it. Signal is OK but I have 3 friends using it, so it's near pointless

I think many people want an alternative to whatsapp and there is not a canonical alternative (telegram maybe used to be but not anymore)

As a daily signal user, I'm not sure signal can really be improved on.

Just use Signal

Lol not important. Im not breaking the law where I need a super private chat app... waste of resources.

I agree with VIF that Proton already offers a wide range of products. However, as a privacy suite aimed at replacing the Apple and Google ecosystems, realistically this is the one thing that they do not have in this space. Im sure it is no small undertaking and would take up resources that could be used elsewhere, but as im sure those of you who have used signal know it is a great communication platform, you also know that it is almost impossible to get people who don't care about privacy and security to switch to it. What I would love to see from Proton is an app that mirrors the functionality of Signal, possibly utilizing the Signal protocol or even the Matrix protocol, but to also support SMS and eventually(if they manage to get a webhook designed to privately use it) RCS. Im sure this would take a lot of work on their end but it would at that point be the go to app for people wanting a full featured privacy messaging app, one that supports their own protocol implementation, allow users to securely communicate securely with RCS and still support everyone that is still hanging on to SMS that they would not even really have to advertise all that much because you know every tech persona would cover all over social media. This would be a Unicorn but if they were to do it they would be the only one and it would be the One stop app for every form of communication giving even more incentive to use their services. Being on Graphene OS this is something I am constantly having to juggle so this would be amazing to see.

... Proton Loom

There is the "matrix protocol", which is open source, allows end-to-end encryption and can be cross-platform in some context

Could this be it (or close)? https://proton.me/meet

Bonjour, je pense qu'il faut avoir une indépendance vis à vis des GAFAM d'USA compte tenu des récentes déclarations américaines. C'est important pour l'Europe. Une alternative à WhatsApp gratuit serait la bienvenue.
Nous, les consommateurs, avons plus de poids que tous les gouvernements.

Threema is the best. Reliable, Secure, Private. If Proton and Threema could collaborate that would be nice. Otherwise, stick with Threema. Signal (free) is a good second choice for to communicate with those who refuse to pay for Threema.

"Signal but better" what's wrong with Signal? Why create another messaging app? That makes no sense. The resources should be used to improve existing products, or create new products that are needed. It's hard enough to get people to switch to Signal, why split the userbase even further?

Yust use Threma

Because I like the proton environment : mail, drive, calendar, docs (when bug will be fixed), I feel like missing a messaging app. Lot of people still use whatsapp because they think they can't create groups with normal sms

there definitely are reasons for "why not", such as requiring ongoing development time that could go into Proton's many already existing products instead.
but also, what's wrong with Signal? or rather, what could Proton do better than Signal that would actually provide meaningful value and not just further fragmentation in the messaging app market? considering most people still just use WhatsApp or maybe Telegram because everyone else does, too, and cross-platform messaging does not exist to my knowledge