A group of brilliant beings who travel together solving other species' problems in exchange for payment, and who coveted Seven of Nine.
The Think Tank was a small collective of exceptionally intelligent individuals from different species who sold solutions to difficult problems. Their spokesman, Kurros, approached Voyager in 2375 while the ship was being pursued by Hazari bounty hunters, offering to help in return for a price.
The price they wanted was Seven of Nine, who they hoped would join them. Janeway refused, and the crew discovered that the Think Tank itself had hired the Hazari to make Voyager desperate. The crew turned the scheme around and escaped both groups.