LoadBalancer/backend protocol synchronization issues (both Resin load balancer and Apache)
@com.caucho.ejb.SessionPool is a class annotation for stateless server beans that specifies the size of the stateless session pool.
HMTP/BAM internal refactor.
Hessian performance improvements to use low-level reflection when possible.

Resin 4.0.2

CanDI updates to match changes to the JSR-299 and JSR-330 specifications.
Servlet 3.0 early access updates
Continued EJB Lite development
Clustered/Cloud .war deployment enhancements, including staging, versioning, and ant/maven tasks.
Regression (QA) cleanup and stress test work to bring Resin 4.0.2 up to a production level.
WebSocket, HMTP and JMTP support.
JMS clustered singleton queue and clustered topics
/resin-admin support for REST-based management tools such as nagios.
Enhanced /resin-admin monitoring to better illustrate the server status.
HTTP Proxy and FastCGI load balancing with failover.
Eclipse plugin enhancements.

Resin 4.0.1

CanDI major refactor to match major changes to the JSR-299 specification.
Servlet 3.0 early access implementation, including replacing Resin's experimental comet support with Servlet 3.0 async
Quercus Pro support for other application servers, and increased support for Google App Engine.
Stability and performance work for clustered caching and sessions