Hi!  This is the jabber service.

help for you

client for Android

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for iOS(iPhone, iPad devices):

download for iOS IM+ client for this service

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for MAC OS:

download for MAC OS Spark client for this service

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for Windows:

download Pidgin client for this service
and install it:

create XMPP account with your login\pass and this server name: imos.tk

connect and apply cert from imos.tk

register client on server

restart Pidgin

that's all))

See also: 

download manual for setup and setting jabber client.