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