Snikket – is an Internet chat service, based on open standards, providing private and secure communication while not depending on phone numbers or a central provider, and can communicate with any other open standard internet chat service. It is available as an app for Android and iPhone, but can be used through any software which supports XMPP.
This article describes how to set up Thunderbird chat with a snikket account, for a user fred.bloggs@snikket.example.org with a password of loquaci0us (you should use a stronger password than this, and specifically do not use this).
Note that Thunderbird does not support some of the features of XMPP, such as OMEMO encryption, or voice of video chats, but it does still allow for basic one to one messaging.
In Thunderbird select Edit/Account Settings which will show a screen with information on your current email account(s) and a button ‘Account Actions’
This gives an option ‘Add chat account…’
Select the XMPP option and click Next
Fill this in as (changing the name and domain as appopriate)
Click next and enter your password on the next screen.
You will be shown some extra options
These allow for special cases, which you can ignore, so just press next and see:
Click Finish and you are there.