After the release of the SharePoint 2013 Server for MSDN and technet subscribers, Microsoft finally released SharePoint Foundation 2013.
Every user is now able to download if from here. If you are using "Microsoft Search Server Express 2010" then you should be known that there will be no "Microsoft Search Server Express 2013". On the Microsoft website you will find the following quote which will prove that:
"The search capabilities of SharePoint Foundation 2013 have changed, and are now based on the same search implementation as SharePoint Server. This provides many improvements, but also means that the search configuration is very different."