The Mother series, known in the West as Earthbound, are some of the best games to ever grace a Game Boy. They're so good, in fact, that Nintendo of America wants nothing to do with them.
Despite years of asking, demanding and then begging for the third game in the series - never released outside of Japan - to be localised for a Western audience, Nintendo of America has not done so.
Sensing that the publisher lacks the will (or the legal clout) to continue the series for American and European consumers, a group of fans have got together and decided to make their own Mother game. And they're calling it Mother 4.
It of course has nothing to do with Nintendo, nor the series' creator Shigesato Itoi. Its developers are just fans, making a pro-active decision that if anybody was going to make a new Mother game that would be playable in English, it may as well be them.
There's no release date or even a guarantee it'll ever be finished (Nintendo having one of the most trigger-happy legal teams in the industry), but if it does make it to a playable state, it'll surely be as a downloadable PC game.
If you think playing Mother 4 without having played Mother 3 will be confusing (Mother 2 was released in the West as "Earthbound"), you could always go and play Mother 3, which received an excellent fan translation a few years back.