So with some delay, the first cumulative update package for SharePoint 2013 Server was recently released
Even though the SharePoint 2013 Foundation CU were available already from 9th of April, you might have awaited the Server packages and/or Project Server packages as well. Luckily, they are out now!
Please find as usual all related information below:KB 2832224 - Office 2013 cumulative update for April 2013
Download SharePoint Foundation 2013 cumulative update package (SharePoint Foundation server-package): April 9, 2013 (Note This is build 15.0.4505.1002)
Download SharePoint Server 2013 cumulative update package (SharePoint server-package): April 26, 2013 (Note This is build 15.0.4505.1005)
Download Project Server 2013 cumulative update package (Project server-package): April 26, 2013 (Note This is build 15.0.4505.1005)
NOTE! In order to install future updates, the March 2013 PU will be mandatory! So you must install these updates on RTM Farms before you can install subsequent updates in the future! (http://blogs.technet.com/b/steve_chen/archive/2013/03/22/3560441.aspx)
As usual, you need to run the SharePoint 2013 Products Configuration Wizard on each machine in the farm after installing the packages.
The SharePoint Server pack contains the Foundation packs, so you basically only need to install one Package. The project Server Packs are containing both, so if you install this one, no need for the other two to install additionally.
For Office Web Apps, Client- and/or Project Server updates, see here: http://blogs.technet.com/b/steve_chen/archive/2013/03/26/3561010.aspx
Other Related Links:
Update center for Office, Office servers, and related products
Build Matrix for SharePoint Server 2013
Build Matrix for SharePoint Server 2010
Build Matrix for SharePoint Server 2007 (aka MOSS)
Project 2013 and Project Server 2013: Language Packs
Common Question: What is the difference between a PU, a CU and a COD?