There is nothing broken in 0.9 which isn't worse in 0.8 so it no longer makes any sense to keep 0.9 on the unstable branch. I'm sure the added exposure of being on a live branch will reveal some things that nobody noticed before, but overall 0.9 is now much more stable than the previous version.
...as such, 0.9 is going to the live branch tomorrow morning. (Friday Sep 24)
Here's a short summary of the changes:
Complete overhaul of save system
The entire world runs on an asynchronous database now. That means the game is smoother and more stable and less likely to lose your data when it crashes.
Resource system
Ships will now require resources for construction. Repairing now requires resources. Get resources from mining, piracy, or trade.
Experience
You can now properly explore the mastery trees because your character gets exp from all sorts of activities.
End game dungeon
The gauntlet is the final challenge in Zero Falls. You may enter with your ship and try to defeat the final boss.
Overhauled damage model
Reworked structure and damage to make ships more survivable and to remove the irritation of having to reach structure requirements in a design
New NPC behaviors
Trade npcs have receive a number of tweaks and there are now mining npcs which will be defended if you choose to mess with them
New home station
It has been streamlined and we have added some new ways to get around it. There are now different areas which can help you accomplish different tasks. Consider checking out the new mining ring subway station, or marvel at our magnificent cloning facilities
New Crew members
There are new recruitable crew members, and they have interesting auras which do different things!
Sensors, clouds, and vision
You can now hide from enemy ships in a cloud, and having better sensors will make a difference in combat.
Communication with NPCs
You can see NPC ships chatting with each other now, and if you like you can hail them and talk to them yourself. You will now need to hail repair stations in order to repair at them
Modding
We've made some big improvements to allow for better mods. The way the game loads assets has been rewritten to support replacing any art inside the existing client, and the engine was enhanced to load dlls from the steam workshop which modify the game's code directly. We also release a very primitive modding library on github which we want to expand on in the future. In theory, anything is now possible for mod makers and it should work with the steam workshop.
Cloud saves
Are cloud saves working now? Probably! We're certainly going to be configuring steam to use them starting with patch 0.9 and we don't anticipate any problems. With characters and worlds being inside database files now it should be a straightforward change to make, but tell us if you have any issues.
Stability and bug fixes
One of the hardest problems for us to solve in this update was just fixing the existing quests. They aren't all 100% working guaranteed at this point, but they were downright unplayable before and we think 0.9 should be a big improvement in this area. We addressed a number of large underlying issues with quest-npc continuity that could cause ships and crew required for quest completion to slip through the gaps of our save system and stop working after a save and a reload. This update post is being posted right now because just last night I was actually able to complete the blockade quest after saving and loading. Individual quests and edge cases may still need to be addressed, but the core underlying framework is now in place.