From time I have been wondering if there is even such thing.
The only one to not being even commercial is FICS which is only free of charge, not as in freedom.
To be exact, I know that ICS protocol is not standard but just wanted to use XBoard and similar clients in places and platforms where Lichess cannot be used.
Isn’t Lichess FLOSS? It’s parts are GPL3 and AGPL3 as far as I can tell. Super popular too.
I mentioned it in the description…
Not sure what you’re looking for then. Do you want one that runs offline?
For example, in Cuba with the big internet prices and low-bandwidth mostly available, something like main Lichess or a self-hosted instance is not reliable enough. iRC is considered the most resource saving software for chats, for example and is very valuable. Email however in plain text has a bigger impact.
Other times, there are computers with resources or an old operating system which cannot load Lichees in the web.
But for all of this, ICS compatible clients work.
I know about Lichess and set in the description that was not valid but wanted to prevent explanation because it is time consuming and out of the point since I already dealed with it.
