Title says it all.
Here are my picks for some technologies that would severely ramp up the danger factor of the Borg in Star Trek that are still attainable by the Collective.

Music from bensound.com, purple-planet.com and freesfx.co.uk
Star Trek Online developed by Cryptic Studios and Perfect World.
Star Trek, Star Trek Enterprise/Voyager/Deep Space Nine/Discovery/Lower Decks/Picard/Prodigy and The Next Generation are all owned and distributed by CBS.
Star Trek Films are owned and distributed by Paramount Pictures
Image stills are from Trekcore
This Video is for critical purposes with commentary.