The only valuable assets on the STEEM blockchain are STEEM and SBD.
Everything else including Actifit and SteemMonsters is at best a way to scam people out of their STEEM and SBD.
Why "at best"?
For example Actifit also seems like an excuse and opportunity to track its users.
Mana also seems like a scam to me, but the currency itself is not even on the STEEM blockchain, but rather a centralized worthless asset.
I remember that I saw someone asking what you asked here already about SteemMonsters.
Guess what?
He was ignored.