The Gateways Editor is now available on Steam, with support for Steam Workshop. Create new levels and share them with the world! We've even added a couple of new achievements for the game related to the workshop.
Any levels you subscribe to through the Steam Workshop will automatically appear in the game in the 'Load Level' menu. As a special treat we've released a new level ourselves called 'Back To The Lab'
If you own Gateways then you should find the Gateways Editor in the 'Tools' section of your Steam library. Publish your level within the editor to release it on the Steam Workshop and let everyone play your creation.