Originally posted by hwa
there's Adabas C from Software AG (SAG) and Adabas D (RDBMS), which is for free with some limitations.
You could visit sapdb.org to find the details. The policy of SAP for sapdb is a open source. But Sap sold sapdb to mysql (mysql.com). The policy of mysql.com is "If you are free. we are free. If you are commerical, we commerical".