Here is the full list of all 20 Manyland achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Save a creation
Create an area thumb
Fill-build by placing the corners of a rectangle in clockwise order starting at the top
Clone a creation by someone else and save it
Play C major using associated keyboard shortcuts
Open friend list which contains a friend
Save an Interacting that checks if someone jumps
Change your body
Save a Writable comment or thread
Create a flying mountable with color trail
Use the move backwards boost
Switch to the alternative color picker
Search for In Bin
Consume a hot edible
Catch item from item thrower
Place a fill light
Attach a motion to the body
Sit down in a created area with 20 or more people around
Place something in a snap to grid holder
Set up a home location using snapshots and transport to it