An FTP server is what an FTP client connects to for file transfers.
There are lots of FTP servers available, but many of them are only usable at a cost.
Below is a list of the bestfreewareFTP server programs that run on Windows, macOS, and Linux.

FileZilla Server
Intuitive interface.
Perform file transfers simultaneously.
Supports secure file transfers.

Bookmarks for fast connections.
Can’t edit files from inside the app.
Does not refresh folder views automatically.

FileZilla Server is an open-source and free server app for Windows.
It can administer a local server as well as a remote FTP server.
Xlight FTP Server
Lightweight.

Supports multiple connections at once.
More difficult to use for FTP novices.
Can be complicated to configure.

The Xlight FTP Server can use SSL and can require clients to use a certificate.
It also supports ODBC, Active Directory, and LDAP authentication.
Xlight is free for personal use only and works with Windows, both32-bit and 64-bitversions.

CompleteFTP
Simple installation.
Supports encrypted file transfers.
More features than most FTP servers.

Full menu hidden by default.
Has occasional performance issues.
Limited features in free version.
CompleteFTP is another free Windows FTP server that supports both FTP and FTPS.
This program has a full graphical user interface and is easy to use.
This program installs as a trial of the professional edition.
Core FTP Server
Quick setup.
Free version only supports three domains.
Core FTP Server is an FTP server for Windows that comes in two versions.
One is a minimal server that’s simple to understand and easy to set up in about a minute.
It’s 100 percent portable and has you choose a username, password, port, androotpath.
There are a few other parameters as well if you want to configure them.
The other version of Core FTP Server is the full-fledged server.
Both versions of this FTP server come as 32-bit and 64-bit versions for Windows.
Vsftpd
Fast FTP server.
Supports secure file transfer.
Complicated to install and configure.
vsftpd is a Linux FTP server that claims security, performance, and stability are its core selling points.
This program is the default FTP server used in Ubuntu, Fedora, CentOS, and other similar OSs.
vsftpd lets you create users, throttle bandwidth, and encrypt connections over SSL.
It also supports per-user configurations, per-source IP limits, per-source IP address configurations, and IPv6.
Refer to thevsftpd manualif you need help using this server.
ProFTPD
More secure than other FTP servers.
Add-on modules available for more features.
Ideal for web servers.
Difficult for novices to install.
Rebex Tiny SFTP Server
Tutorials available.
Simple to configure (no setup required).
Minimalist, with few advanced features.
Requires .NET 4.0
Windows only.
This Windows FTP server is lightweight, portable, and can get up and running in seconds.
Just unzip the program from the download and selectStart.
The only downfall with this program is that you must make any configs adjustments through the RebexTinySftpServer.exe.configtext file.
After extracting the ZIP file’s contents, use the RebexTinySftpServer.exe file to kick off the program.