Complex sentence: It was an open-sourced version of the earlier StarOffice, which Sun Microsystems acquired in 1999 for internal use, then open-sourced in July 2000 as a competitor to Microsoft Office, releasing version 1.0 on 1 May 2002.
Split into simpler sentences: It was an open-sourced version of the earlier StarOffice, which Sun Microsystems acquired in 1999 for internal use. Sun open-sourced the software in July 2000 as a competitor to Microsoft Office, releasing version 1.0 on 1 May 2002.