The code is clean and is written with n-Tier architecture in mind (distributed architecture).
OpenFramework is stable and well tested, it runs behind of many websites and web applications with million visitors per day.
OpenFramework is intended for professional developers, featuring a Multi-Tier (n-Tier) architecture which is DISTRIBUTED, much FASTER and more SCALABLE than MVC.
The advantages of Multi-tier architecture (n-Tier) against MVC are here:
PHP Framework – OpenFramework Web Site