Space Engineers will have a public Multiplayer test on June 2. 

It will start at 11AM CET, and end at 5PM CET. You'll need to activate a BETA Branch, which can be done by these steps:

1. Right click on the game, select properties

2. Click the BETA's Tab

3. Fill in this code in the text field: nt7WuDw9kdvB

This Multiplayer test is to check how stable the game has become, and see if some bugs are fixed.