The packages:

com.hazelcast.internal.util.collection
com.hazelcast.internal.util.concurrent

and the classes:

com.hazelcast.internal.util.QuickMath
com.hazelcast.client.impl.protocol.util.UnsafeBuffer
com.hazelcast.client.impl.protocol.util.BufferBuilder

contain code originating from the Agrona project
(https://github.com/real-logic/Agrona).

The class com.hazelcast.internal.util.HashUtil contains code originating
from the Koloboke project (https://github.com/OpenHFT/Koloboke).

The class classloading.ThreadLocalLeakTestUtils contains code originating
from the Tomcat project (https://github.com/apache/tomcat).

com.hazelcast.internal.cluster.fd.PhiAccrualFailureDetector contains code originating
from the Akka project (https://github.com/akka/akka/).

The package com.hazelcast.internal.json contains code originating
from minimal-json project (https://github.com/ralfstx/minimal-json).

The class com.hazelcast.instance.impl.MobyNames contains code originating
from The Moby Project (https://github.com/moby/moby).

The class com.hazelcast.internal.util.graph.BronKerboschCliqueFinder contains code
originating from The JGraphT Project (https://github.com/jgrapht/jgrapht).

The packages:
com.hazelcast.sql
com.hazelcast.jet.sql

contain code originating from the Apache Calcite (https://github.com/apache/calcite)

The class com.hazelcast.jet.kafka.impl.ResumeTransactionUtil contains
code derived from the Apache Flink project.

The class com.hazelcast.internal.util.ConcurrentReferenceHashMap contains code written by Doug Lea
and updated within the WildFly project (https://github.com/wildfly/wildfly).

The classes:
com.hazelcast.cp.internal.raft.impl.state.FollowerState
com.hazelcast.cp.internal.raft.impl.state.FollowerStateTest
com.hazelcast.cp.internal.raft.impl.SlowFollowerBackoffTest

contain code originating from the MicroRaft project (https://github.com/MicroRaft/MicroRaft)