BOSTON CTLR OBSERVES WRONG ACFT BEGIN TKOF ROLL AFTER TKOF CLRNC WAS ISSUED TO ANOTHER ACR DEPARTING FROM ANOTHER INTERSECTING RWY AND ISSUES ABORT CLRNC.

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ACFT #1 POS AND HOLD ON RWY 22R. HE WAS TOLD TFC WILL DEPART XING RWY AND CROSS DOWNFIELD. CROSSED ACFT MIDFIELD. CLRED ACFT #2 FOR TKOF RWY 15R; THEN CONTINUED TO TALK TO ACFT ON RWY 22R INBOUND. BOTH ACFT #1 AND #2 ARE ROLLING. CANCELED ACFT #2 FOR TKOF. ACFT #1 WAS NOT LISTENING TO MUCH OF ANYTHING THAT WAS GOING ON. ALL OF THE ABOVE XMISSIONS HAPPENED IN LESS THAN 1 MIN. ACFT #1 COULD HAVE HIT THE DEPARTING ACFT #2 AND THE 3 THAT WERE XING DOWNFIELD. VERY; VERY IMPORTANT THAT AT LEAST 1 PLT IN THE COCKPIT SHOULD BE PAYING ATTN TO WHAT IS GOING ON AT THE ARPT AROUND THEM. ACFT #1 JUST HEARD CLR FOR TKOF AND ROLLED. THEY HAD NO IDEA WHAT ELSE MIGHT HAVE BEEN GOING ON. IF THEY HAD; THEY WOULD HAVE KNOWN THE ACFT #2 WAS CLRED FOR TKOF ON THE XING RWY; LIKE HE WAS TOLD WHEN THEY WERE TAXIED INTO POS AND HOLD ALONG WITH KNOWING THAT SEVERAL OTHER ACFT WERE XING HIS RWY; WHICH THEY ALSO WERE TOLD ABOUT THE ACFT #1 HOLDING IN POS ON RWY 22R. LISTEN TO THE FREQ AND KNOW WHAT IS HAPPENING TO YOUR RWY AND AREA AROUND YOU. THIS COULD HAVE BEEN EXTREMELY FATAL IF ACFT #2 WAS UNABLE TO ABORT HIS TKOF AND THE OTHER XING ACFT TOOK THEIR TIME.