Very interesting table, Vertograd. According to Wikipedia, Oracle is written in Asm :shock:, c, c++.
In the other hand PostgreSQL is used by Yahoo! managing 2 Petabytes of data. Not bad, besides it allows commercial or non commercial usage. That's not bad, I think.
For little projects (the most common, I guess), maybe SQLite is enough, and is used by many large companies. Not bad neither.
Firebird is a fork ob Interbase, with full support for stores procedures and triggers. It also allows to make proprietary software based on it (maybe a bit more restricted than Postgres?)
All of them have full connectivity apis for java, c, etc. Not bad... Maybe I'll have a look to Firebird, just for curiosity, but Postgres and SQLite seem to be just what I need.
Regards.