sakupljati

1. to collect; to gather
   Moj deda sakuplja stare marke. — My grandpa collects old stamps.
   Deca su sakupljala lišće u parku. — The children were gathering leaves in the park.
2. (of money, data) to collect; to raise
   Sakupljamo novac za lečenje devojčice. — We're raising money for the girl's treatment.
3. (sakupljati se) to gather; to assemble
   Ljudi su se sakupljali ispred Skupštine. — People were gathering in front of the Parliament.

The perfective is "sakupiti"; in speech "skupljati" is more frequent.