Version 0.6 of Planet Explorers has been released yesterday. Now the game is no longer free to play.
If you want to continue to play to Planet Explorers, you need now to pre-order it to receive an alpha key. The game cost currently 21$ and you can pre-order it here: http://planetexplorers.pathea.net/order/
This new version is only for Windows but versions for Linux and Mac are coming later this week.
The changelog is really long, so we invite you to read it here: http://planetexplorers.pathea.net/alpha-0-6-released/