Is there a specific reason to want to use a commercial product? There are many opensource solutions with equal or better features and stability. (implied by user scale)
Note that the source editions - according to their website also advertise Lazarus as a target (probably only windows), so contact the nexusdb and ElevatDb service desk.
I always prefer open source solutions, but I didn't find the features that I need.
MariaDB and PostgreSQL are great databases but to heavy for my needs.
SQLite is not client-server, so it seems that FirebridSQL is closest to NexusDB regarding the size and features.
The reason why I chose NexusDB instead of Firebird 15 years ago is that NeuxsDB support cross-database query,
"select into #table" syntax with (#context-local, ##session-local and ###global temp. tables) that is great for reporting,
you can mix memory tables with ordinary tables and everything is written in object pascal.
In the meantime, FirebirdSQL has progressed but still doesn't support those features.
Seems that I will go with Firebird.
If you know any other similar relational open-source database, I would like to test.