Firebird is a universal open source database.
This review is dedicated to the 10th anniversary of the fire bird (to be held in July), as well as the imminent release of the final version of Firebird 2.5 (most likely the end of April - the beginning of May).
MindTheBird!
www.MindTheBird.com

There are many reasons to think about Firebird ...

• 1+ million Firebird developers
• 2500+ daily installations on Windows, not counting Linux installations
• Millions of Firebird copies are installed along with boxed applications (ISV)
• Firebird is included in all major Linux distributions and repositories.

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Firebird is ...

multi-version architecture

• Hybrid applications
  The multi-version architecture allows creating Firebird-based systems for one-time online data processing (OLTP) and report generation (OLAP)
• Automatic version control
  Firebird automatically sweeps as needed (known as vacuum in other DBMS)

events

Events

• Event notifications can be sent from triggers, stored procedures, and execute blocks.
• Flexible subscription mechanism
  -ON TRANSACTION START (at the start of the transaction)
  -ON TRANSACTON COMMIT
  -etc
  

Logging and synchronization

• Instant database-level event notifications can be triggered (and logged) from database-level triggers.
  -ON CONNECT (per connection)
  -ON DISCONNECT (detachable)
  -etc
  

powerful sql features

• High compatibility with ANSI SQL
• Common Table Expressions (CTE)
• Flexible transaction management
• Powerful stored procedures (selective procedures allow joins to tables within a single SELECT)
• Queries to multiple databases

trace api

Trace API

• Real time monitoring
• Debugging SQL Queries

Audit

• Developments
• Partial or full protocol SQL
• Through remote connections!

security

SQL level security

• Users and Roles
• Setting permissions for all basic operations with data and database objects
• DB Owner's Concept

Windows Trusted Authentication

• Single sign-on on Windows and client program
• Integration with Windows domains and Active Directory

Network

• Only one port is required (3050 by default, configurable)
• Aliases hide real database file paths

4 architectures

• Classic
  Architecture for powerful systems with multiple CPUs and lots of RAM
• Superserver
  Compact and high-performance version for embedding in replicable software
• Embedded
  Single-user DBMS in a DLL. Transparent migration to older versions!
• Superclassic
  New architecture in 2.5! The combination of the best from SuperServer and Classic. Ideal for virtualization

scalability

• 4 architectures allow you to create databases from 1MB to 1TB
• From 1 user to 1000
• From DLL to multiple CPUs

multiplatform subd

• Support for Windows, Linux, HP-UX, Solaris, Mac OS X, FreeBSD, etc.
• 32 and 64 bits
• 100% OS compatibility and one-step cross-platform migration

development tools

• Firebird.NET
• Jaybird (java)
• UIB, FIBPlus ^* , IBObjects ^* (Delphi / C ++ Builder)
• FreePascal & Lazarus
• PHP for Firebird
• FireRuby
• and not only!

^* - commercial software

confident movement

• Over the past 12 months, Firebird has been installed on Windows 672114 times (fixed by a link to the web page of the official site from the installer). Or - 1800 installations every day for the last year (from 1500 a year ago to 2500 now). The number of installations on Linux (and others.), Embedded or own installers are not tracked.
• www.firebirdsql.org - 7,000 unique visitors per day, and 1.8 million visitors per year
• 6,583,438 downloads since 2000 only from sourceforge.net
• Included in the repositories of all major Linux distributions (Mandriva, Fedora, Debian, OpenSuse, etc.)
• Annual use growth + 10%
• Development since 2000: 5 releases (1.0, 1.5, 2.0, 2.1, 2.5) and a clear development plan (3.0 is in alpha testing)
• 12 active kernel and driver developers
• A large community around the world:
  Brazil
  Germany
  Russia
  USA
  Australia
  Italia
  France
  Turkey
  Spain
  other!
  

References:

• www.mindthebird.com
• www.ibphoenix.com
• www.firebirdnews.org
• www.firebirdsql.org
• www.ibase.ru
• www.ibase.ru/webinar.html - webinar, review of new features of Firebird 2.5

PS
In addition, the main developers are our compatriots, with whom you can communicate in their native language. For example, here: www.sql.ru
Pps
If interested, then there is an almost complete review of Firebird's competitors and a comparison with the Bird.