In an ideal world:<p>- open source, client and server<p>- federation (both for the ability to split the net&#x2F;have a private&#x2F;enterprise solution and for redundancy)<p>- multi device support (tablet, phone, desktop etc)<p>- clients for all major platforms (that is, not just mobile platforms)<p>- strong cryptography<p>- no phone number required (can be installed on your desktop&#x2F;tablet only, doesn&#x27;t _need_ a phone number but might offer to search for contacts that gave one instead)<p>Note that Telegram fails quite some of those, but as far as I&#x27;m aware it&#x27;s the closest I can get at this point.