Vielleicht ist NexusDB nicht die schlechteste Alternative, wenn man deren Wurzeln einmal ansieht:
https://www.nexusdb.com/support/index.php?q=node/506
"While NexusDB is a completely newly designed product its conceptual foundations date back to 1986. At this time, ENZ, a German company, created a product called BTreeFiler for Turbo Pascal. BTreeFiler was a file-based database system which used the server purely as a file server. In time, Turbo Power sold BTreeFiler under license for ENZ. Turbo Power eventually bought BTreeFiler outright from ENZ."
Achso, wenn schon TurboPower BTreeFile genannt wird, dann gibt es ja auch noch das hier als Opensource:
https://sourceforge.net/projects/tpbtreefiler/