what is the diffrence between openstack and encalyptus

Differences in features: http://wiki.openstack.org/Nova/EucalyptusFeatureComparison

Reasons why i joined openstack project, in no particular order, all of them are important a lot for me and for most of them i could not find another project being at least half that good:
* Free/Open spirit: http://wiki.openstack.org/Open
* http://wiki.openstack.org/BasicDesignTenets (reading this page told me a lot about authors)
* Python, very readable, adaptable, extendable code. See also http://www.ohloh.net/p/novacc/factoids/4030902
* AMQP for async operations
* Large number of notable companies are joining -- http://www.openstack.com/community/
* IRC channel -- many very smart and friendly people are here, having the right mood (!)
* Very large active development team -- http://www.ohloh.net/p/novacc/factoids/4030901

To be fair, what i do not like on openstack:
* documentation is still very sparse. It is improving now, but still its not good enough.
* live migration support is what i would love to see working (its coming, but not yet there)
* i would love to see sheepdog or similar system integrated already (again, there are people working on that)

To sum it all: OpenStack is still very young, but it is clear to me that this project will win in the longer run. When i understood that there is no viable alternative, i decided to join the winning team.