Freeplay mode with unlimited items

[Zirr]

I would really love this. Just basically everything researched, instant crafting, unlimited health and items. Perhaps also the ability to change between freeplay mode and normal mode.
Maybe a setting in options or something like that.

[Poiasdope]

An alternative to what you want is the map editor mode. You can generate a map and edit it using the 'E' key to open the menu. Have fun!

[kovarex]

Sandbox (creative mode) is planned.

[Cordylus]

Implemented in 0.5.0