jFTPd is a free, pure java FTP server and runs on almost every platform where Java VM is available. Currently it runs on Microsoft Windows, Sun Solaris and Linuxes. It needs JDK 1.5 to run.
It was initially designed with simplicity in mind FTP. However, it evolved in time to become a highly stable FTP server (thousands of connections per day) with huge uptime (in fact it runs as long as the machine runs).
Its advantages are:
1. RFC compliance.
2. SSL Implicit support (firewall friendly, supports the CCC command)
3. Handles huge files (2Gb).
4. Can open passive ports only in a given range.
5. Can limit the maximum number of users logged in at a given time.
6. Can resume uploads/downloads.
7. Runs as a service on Windows 2000/XP machines, using JVMI 1.3
8. Low memory profile.
9. It is able to upgrade itself to a newer version by preserving all the settings.