how about the EJB3, is it necessary to use it in small application ?
EJB3 is optional, Seam works fine with JavaBeans.
Anyone have small seam app sample that deployed under tomcat?
Take a look at the seam jpa booking example (seam/examples/jpa/):
This is the Hotel Booking example implemented in Seam POJO and Hibernate JPA.
It can be deployed in JBoss AS 4.x, WebLogic, GlassFish, Tomcat (both with and
without the EJB3 container).
For a more complex example, see the demo application of 'Seam in Action': Open18. I think, it does not require EJB3, too.
Yes i did develop one (much more than one actually), and I think that Seam is EVEN better if you plan to use tomcat. Go without fear. If you plan to use JSF, i would say that Seam is ALWAYS the best choice. :)