Alpha/Beta (development) stage 2D isometric roleplaying universe now accepts bitcoins as well as various alternate block chain currencies based on bitcoin code.
Accessible using Crossfire RPG clients such as the java one whose daily build is at http://invidious.meflin.net/jxclient.jar
The clients use a metaserver to find out what servers are out there, ours is listed as Crossciv, Freeciv Galactic Milieu.
But, it has fantasy as well as science fiction milieus. Using the old classic character-creation method where creating your character is done on the server you choose milieu buy your choice of race/species and profession, basically anything other than a non-magical human is considere fantasy and lands on a fantasy world instead of in the science-fictional galactic milieu.
The newfangled character creation method where race and profession and stats are all done in the client kind of messes with that currently, as the programmers didn't realise anyone was actually using the ability to steer characters to different starting locations based on their race and profession. So until some mechanism is added for filtering access to areas based on race and profession anyone using the newfangled, client-side character-creation routine ends up in the fantasy world even if they are a plain old non-magical human thief swashbuckler ninja warrior barbarian etc.
(Like I said it is still in development...