1. Scalability and Performance: Apache Pulsar is designed to provide high scalability and performance for messaging and streaming workloads. It provides features like scalable persistent storage, multi-tenancy, and low latency. On the other hand, Scheduler API is primarily focused on scheduling and task execution, rather than messaging. It provides mechanisms to define task dependencies and execution plans.

2. Messaging and Streaming Capabilities: Apache Pulsar is a powerful messaging and streaming platform that supports publish-subscribe, queuing, and real-time streaming with exactly-once semantics. It provides features like message replay, durable storage, and event time processing. Scheduler API, on the other hand, does not have built-in messaging and streaming capabilities. It focuses more on managing and executing tasks based on predefined schedules.

3. Flexible Task Scheduling: Scheduler API provides a flexible and extensible framework for defining task schedules. It allows users to define complex schedules using cron expressions, as well as create custom scheduling strategies. Apache Pulsar, on the other hand, does not provide built-in task scheduling capabilities. It is more focused on messaging and streaming.

4. Fault Tolerance and Resilience: Apache Pulsar is designed to be highly fault-tolerant and resilient. It provides features like automatic data replication, data recovery, and seamless failover. Scheduler API does not have built-in fault tolerance mechanisms. It relies on external systems for ensuring fault tolerance and resilience.

5. Integration with Other Systems: Apache Pulsar provides seamless integration with various other systems and frameworks, such as Apache Kafka, Apache BookKeeper, and Apache Flink. It allows users to easily consume and produce data from/to these systems. Scheduler API, on the other hand, does not have native integration capabilities with other systems. It focuses more on task scheduling and execution.

6. Community and Ecosystem: Apache Pulsar has a thriving community and ecosystem with active contributors and a wide range of third-party tools and libraries. It is used by many large-scale organizations for their messaging and streaming needs. Scheduler API, on the other hand, may have a smaller community and ecosystem, depending on the specific implementation or framework used.

In Summary, Apache Pulsar is a highly scalable messaging and streaming platform with advanced features for fault tolerance, integration, and performance. Scheduler API, on the other hand, focuses more on task scheduling and execution, providing a flexible framework for defining schedules and executing tasks.