Here is the full list of all 21 Intralism achievements.
Win multiplayer match
Create new level in editor
Up your profile to level 10
Play 5 maps in relax mode
Complete 10 (different) official maps in normal mode
Play multiplayer game with other player
Play multiplayer match with workshop level
Complete level in multiplayer
Find authors list
Swich workshop filter in maps list from "trend"
Play multiplayer game alone
Recieve your rank
Find your items
Subscribe to any level in workshop
Lose within second after checkpoint and resume from it
Launch Intralism
Collect at least one item of each rarity