What are the differences between rdesktop and xfreerdp?

FreeRDP (xfreerdp, whose Debian package name is freerdp-x11) was, in 2015, considerably less used than rdesktop according to the Debian Popularity Contest stats, in part because it was so much newer:

#rank         name  inst vote   old recent no-files (maintainer)
1429      rdesktop 56497 4281 41399  10775       42 (Laszlo Boszormenyi)
3056   freerdp-x11 14232 1389  9845   2992        6 (Mike Gabriel)

However, as of 2020, that is no longer true:

#rank         name  inst vote   old recent no-files (maintainer)
 4439  freerdp-x11 11869  582 10856    426        5 (Not in sid)
 4597     rdesktop 11099 1191  9443    458        7 (Laszlo Boszormenyi)
 7319 freerdp2-x11  3891  704  1500   1686        1 (Debian Remote Maintainers)

The old freerdp-x11 package, removed from Debian in Feb 2018, outranks the older rdesktop while its replacement, freerdp2-x11, still has some catching up to do. I assume the smaller install count is the result of fewer people actually needing this Windows-only solution or perhaps a hint of xpra and other next-gen solutions taking over.

According to FreeRDP on Wikipedia,

FreeRDP was forked in 2009 from rdesktop with the aim of modularizing the code, addressing various issues, and implementing new features.

... but Wikipedia's list of features do not break out which came from rdesktop and which are "new." The FreeRDP 1.0 release announcement (Jan 2012) did offer this list of new features, which presumably are not also available on rdesktop:

• RemoteFX
  • Both encoder and decoder
  • SSE2 and NEON optimization
• NSCodec
• RemoteApp
  • Working, minor glitches
• Multimedia Redirection
  • ffmpeg support
• Network Level Authentication (NLA)
  • NTLMv2
• Certificate validation
• FIPS-compliant RDP security
• new build system (cmake)
• added official logo and icon

FreeRDP also has a server (listed as experimental in the 1.0 release) while rdesktop does not.

For anyone coming to this:

Among all rdp clients out there, which i tried, when connecting to windows server on azure, all worked except rdesktop which seems to have problem with recent protocol version. See here https://bugzilla.redhat.com/show_bug.cgi?id=1075697 → uninstall!

freerdp (xfreerdp on debian) rocks. Check their github https://github.com/FreeRDP/FreeRDP

Other answers to this question fail to point out that freerdp appears not to work with Windows NT 4.0 Terminal Server:

• FreeRDP Issue 1189
• FreeRDP Issue 183

On the other hand, I have successfully used rdesktop (w/grdesktop) to connect to Windows NT 4.0 Terminal Server.