I'm using Sharepoint Foundation 2013 and i'm looking for an alternative to Design Manager, which is not included into foundation. Since i don't have the HTML version of the master.page and i'm a bit new to sharepoint it would be quite diffucult to do it without an alternative to Design Manager.
You can use Sharepoint Designer. Copy one of the existing Sharepoint masterpages to start from. Connect to site using SP Designer or Map network drive to site and edit files in your favorite IDE.
and here: branding sharepoint foundation 2013