1. Collaboration Features: Notable offers real-time collaboration tools such as commenting and marking up documents, enabling a seamless collaboration workflow among team members. ProofHQ, on the other hand, focuses more on review and approval processes, providing extensive workflow features for managing the review cycle effectively.

2. Customizability and Branding: Notable allows users to customize the layout and design of the platform to match their brand identity, offering a more personalized user experience. In contrast, ProofHQ prioritizes standardization and consistency in the review and approval process, limiting the extent of customization options available.

3. Integration with Other Tools: Notable provides integrations with various third-party tools and services, allowing users to enhance their workflow by connecting different systems seamlessly. ProofHQ, however, offers a more closed ecosystem, with limited integration options available for external software.

4. Cost Structure: Notable follows a subscription-based pricing model, offering different plans tailored to the needs of individual users or organizations. In contrast, ProofHQ typically involves a more structured pricing system, often based on the number of users or the level of functionality required.

5. Usability and User Interface: Notable prioritizes a clean and user-friendly interface, making it easy for users to navigate and utilize the platform efficiently. ProofHQ focuses on providing a robust set of features for managing review and approval processes, sometimes leading to a more complex user interface.

In Summary, Notable and ProofHQ differ in collaboration features, customizability, integration options, cost structure, and usability, catering to different preferences and needs in document review and approval workflows.