1. Data Collection: The key difference between Open PostgreSQL Monitoring and PgSync lies in their data collection methods. Open PostgreSQL Monitoring utilizes a network of monitoring agents to collect data from PostgreSQL servers, whereas PgSync relies on log shipping to replicate data changes from one PostgreSQL server to another.

2. Monitoring Capabilities: Open PostgreSQL Monitoring offers a comprehensive set of monitoring capabilities, including monitoring of database performance metrics, query performance, and system health checks. On the other hand, PgSync primarily focuses on real-time replication of data changes between PostgreSQL servers and does not offer the same level of monitoring features as Open PostgreSQL Monitoring.

3. Interface: Open PostgreSQL Monitoring provides a user-friendly web interface for configuring monitoring settings, viewing real-time monitoring data, and generating reports. In contrast, PgSync is primarily configured through command-line interfaces and configuration files, which may require a higher level of technical expertise to set up and manage.

4. Scalability: Open PostgreSQL Monitoring is designed to scale easily to monitor multiple PostgreSQL servers in a distributed environment. PgSync, on the other hand, is more suitable for replicating data changes between a limited number of PostgreSQL servers and may not be as scalable in larger environments.

5. Compatibility: Open PostgreSQL Monitoring is compatible with a wider range of PostgreSQL versions and operating systems, making it a more versatile choice for monitoring PostgreSQL databases. PgSync may have limitations in terms of compatibility with certain PostgreSQL versions or operating systems, which could impact its suitability for certain environments.

6. Community Support: Open PostgreSQL Monitoring has a larger community of users and contributors, providing a wealth of resources, documentation, and support for users. PgSync may have a smaller community of users and developers, which could impact the availability of support and resources for users seeking assistance.

In Summary, the key differences between Open PostgreSQL Monitoring and PgSync lie in their data collection methods, monitoring capabilities, interface, scalability, compatibility, and community support.