Hi Kedar,
As far as I know there is not a trial version of the Open Server. You can try the SDK for SAP ASE but it is missing the libsybsrv binary which is the primary binary in OpenServer.
You can talk to your sales person and see if they get you a trial version of the Software.
If you want to look at the SDK for SAP ASE. At the end of this blog tells you how to get the free SDK, this became available toward the mid year of 2014:
http://scn.sap.com/thread/3360231
Thanks,
Dawn Kim
.