YugabyteDB is designed for high availability and absolute consistency, offering synchronous replication of writes to at least two nodes in the cluster, resulting in low latency strongly-consistent reads and automatic failover. In contrast, PostgreSQL uses asynchronous replication with a master-slave configuration, which can lead to higher latency and unavailability, while MongoDB's asynchronous replication approach also results in high latency for strongly consistent reads. YugabyteDB supports ACID transactions, including single row and multi-shard transactions, whereas PostgreSQL and MongoDB do not support distributed transactions on multiple shards. Overall, YugabyteDB is a high-performance distributed SQL database that combines the best of PostgreSQL and MongoDB into a single database.