Signal is a messaging application. It can be downloaded on Apple, Android, Mac and Linux devices. The app is developed by Signal Foundation and Signal Messenger LLC. WhatsApp co-founder Brian Acton and current CEO of Signal Messenger Moxie Marlinspike are the founders of this organisation.
Secure messaging, voice and video calls with end-to-end encryption is available on this app. We can create groups also on this app. But you may not be able to forward to multiple people at one time, I think. There is a group chat feature also on this app. The group can have members up to 150. But one advantage here is the group can't add any person without the consent from the member. If somebody wants you to join in a group, they will forward an invite to you and then you have to accept. Then only you can be a member of that group. It has a note to the self facility also and you can send notes to your self and store in that.
You can relay your voice calls to app servers to conceal your identity from your contacts. This app will not ask as many details as asked by WordsApp. WhatsApp collects your data which includes device ID, user ID, phone number, email address, contacts etc. But SIgnal asks only mobile number. End-to-end encryption is also available. Sealed Sender feature is also there in this and no one can figure out who is sending and receiving messages.
So security is much better on SIgnal and many people are shifting to SIgnal from WhatsApp recently.