Grimaldi, 21, comes off a season in which he led the University of North Dakota with 17 goals and 22 assists as it reached the NCAA Frozen Four semifinals. He was named MVP of the NCAA Midwest Regional after helping UND defeat Wisconsin and Ferris State.
"We are very pleased to have reached a contract agreement with Rocco," Panthers general manager Dale Tallon said. "He is a hard-working forward who possesses speed along with great vision on the ice. We look forward to his continued growth and development within our organization."
Grimaldi was a second-round pick (No. 33) of the Panthers in the 2011 NHL Draft. He had 31 goals and 77 points in 86 games for UND. As a freshman, his 36 points placed him third nationally and he was selected to the ALL-WCHA Rookie Team.
Grimaldi won a gold medal with the United States at the 2013 World Junior Championship, scoring the game-winner in the championship game against Sweden. He also won a gold medal at the 2010 Under-18 World Championship.
A third-round pick (No. 74) of the Stars in the 2012 NHL Draft, Lindell, 19, had five points (two goals), 10 penalty minutes and a plus-8 rating in 44 games for Jokerit in the Finnish Elite League this season.
He represented Finland in the 2014 IIHF World Junior Championship, where he was tied for second among defenseman with five points in seven games to help Finland win their first goal medal since 1998.
Lindell led the Finnish Elite Junior League with 51 points (21 goals) in 48 games of the 2011-12 season, when he was selected to the league's All-Star team and named the Best Player of the Regular Season.
Aberg, 20, is coming off his first season with Farjestads BK of the Swedish Hockey League. He ranked second on the team in goals (13) and points (31).
In 2012-13 with Djurgarden, the 5-foot-11, 199-pound wing led the Swedish second division (Allsvenskan) junior players with 40 points (12 goals).
Nashville's first choice in the 2012 NHL Draft (No. 37, second round), Aberg was a finalist for the 2012 Swedish Elite League Rookie of the Year.