Is there any alternative for WSO2?
not realy, but some products close to (commercial open source only)
- Mule ESB...
- Sopera (bought by talend, last month)
- Fuse ESB...
as far as I know the SOA-World, WSO2 products are unique in terms of
- complete Open Source infrastructure for SOA + cloud PaaS
- all products licensed under Apache Software License
- not only libraries, but web-GUI, DEV-Tools and OSGi-P2 repositories
- you can follow the public mailing-lists (tip: carbon-dev and architecture)
- conforms to a lot of WS-standards
some drawbacks
- very active development at WSO2, not easy to follow
- some products in a early stage