The former Chelmsford City striker - who has previously played in the EFL with Colchester United and AFC Wimbledon - has penned a deal at the club for the new season.
Folivi netted six goals in 14 games for Vanarama National League South rivals Chelmsford last season.
The club also added Taylor Maloney while confirming a return for Ricky Holmes.
"Wow, just wow," Spencer Day, speaking about the signing of Folivi, told the club's website.
"Buzzing to get Michael. A pacy striker who scored regularly in the EFL before a shocking injury.
"As he showed at the end of last season, including against us, what a striker he is and with Alfie [Pavey] has the real prospects of a lethal partnership.
I’ve no doubt he won’t be with us long and thrilled he chose us after a great conversation.
"Thanks to his agents too who appreciate what Boro can offer Michael on his path forward whilst being fantastic for us."
Folivi added: "It all picked up on Saturday to be fair.
"I had a great conversation with the Gaffer and he sold it to me.
"I see myself kicking on from here and doing good things for the Club. We’ve both got the same vision and that’s obviously to succeed."