As of today, Spigot 1.14.4 is the default Minecraft version built by BuildTools.
As usual you can access older versions by using the --rev flag.

Make sure that you keep backups and thoroughly test your server when updating across large numbers of builds - this can, and do change.
Please direct all discussion to the forums at large, or the 1.14.4 release thread.

If you have a bug report to make, you should please do so using the bugs tab above (please read the guidelines when prompted to do so).

In order to get 1.14.4, simply run the latest BuildTools.
Code (Text):
java -jar BuildTools.jar
If you haven't used BuildTools to create a server jar yet, it is suggested you first read the 1.8 announcement and the additional BuildTools info thread.

A short while ago Mojang released Minecraft 1.14.4 to which Spigot & BungeeCord are now updated.

As this is the final (planned) version for 1.14.x, it will be made the default in the coming week. In the meantime you can retrieve it by running BuildTools with the appropriate arguments.

If this is your first time using Minecraft 1.14.x, please also ensure you read the original release notes first: The additional information from 1.14.1-1.14.3 may also be helpful:

Code (Text):
java -jar BuildTools.jar --rev 1.14.4
If you haven't used BuildTools to create a server jar yet, it is suggested you first read the 1.8 announcement and the additional BuildTools info thread.

BungeeCord can be found as usual on Jenkins.

With the availability of development builds for Minecraft 1.14.3, I would like to take this opportunity to provide some key information that supplements what has already been said about 1.14.

Minecraft 1.14 Information (Read First!):

In particular, it is often still asked "when will Spigot 1.14 be released?". The simple answer to this question is that it is already available for public access. The more nuanced answer is that it is available as a "development build". The characteristics of a development build include the following:
  • It is not the default version available. You are required to use the --rev argument to BuildTools to retrieve it.
  • It is aimed primarily at developers and experienced server owners.
  • There is a higher than usual chance that running such a version may cause irreparable damage to your map. Even if the damage is not irreparable, it is unlikely that attempts to fix such damage will be made - you must restore from a backup.
  • The usual API stability guarantees do not apply. A previously valid plugin using new API features may be broken from one build to the next.
  • Similarly a previously valid server configuration may not be valid in a later build.
    • eg the current requirement that all world names be lower case
  • Updates are very frequent, usually several versions a day.
The followup question is usually "well when will it not be a development build?". In 1.13.x we tried a graduated colour system of stability, but for various reasons this did not work out. Instead for 1.14.x we suggest that you take a look at the Spigot (and to a lesser extent Mojang) issue trackers to decide when the build is right for you, keeping in mind the above points.

In terms of upgrading the build to "default" status, this is done very...
Dear SpigotMC Community,

It is my pleasure to announce that development builds for the Minecraft 1.14.4 are now available. Hopefully most of you are now familiar with how these releases work, so I will try to be brief with the details, but please still make sure you read this post in its entirety.

This is a Development Build
The software released today is the product of several months work. Although the API changes are small compared to 1.13, this is not a small release. In fact it is almost as large as 1.13. Accordingly the software has no doubt inherited many bugs from Vanilla and a few of its own, meaning it is not ready for use on a production server. If using this software you must keep backups, and you must be prepared to use them. As always, downgrading is not possible, and successful upgrades from development versions are not assured either.

Although upgrades from between any two version pairs are technically possible, it is recommended that all upgrades are conducted from 1.13.2. This means that you should first upgrade your world completely on 1.13.2 using the --forceUpgrade server argument, and then do the same on 1.14.

A Note on CraftBukkit
It has come to my attention that many users are running the craftbukkit.jar produced by BuildTools rather than the spigot.jar. The two different jars exist for a variety of (primarily development-related) reasons, however it must be made clear that Spigot is the supported product on Starting from 1.14 BuildTools will no longer be copying CraftBukkit jars to the output directory, however you may still find them in CraftBukkit/target for the time being. If you feel there is some sort of incompatibility preventing you from using Spigot, then you should treat this is a bug and open a report accordingly.

Bug Reports
Every release I make a statement about bug reports, and every release people...

This is a message to let you know that Ubuntu has recently pushed what appears to be a bad kernel update to Ubuntu 18.04 users.

If you are using Ubuntu 18.04, please note that the following kernel appears to have issues handling console input:
4.15.0-44-generic #47-Ubuntu SMP Mon Jan 14 11:26:59 UTC 2019.

Older (e.g. 4.15.0-43-generic #46-Ubuntu SMP Thu Dec 6 14:45:28 UTC 2018) kernels are not affected.

If you are using this kernel and have a message along the lines of " Resource temporarily unavailable", this is the reason.

We are still investigating the exact cause / reason for this.

If you are affected by this issue there are a number of workarounds available (you only need to use one).
  1. Spigot / BungeeCord: Add -Djline.terminal=jline.UnsupportedTerminal to your Java arguments
  2. Spigot: Add --nojline to your Spigot arguments
  3. Reboot your server and select 4.15.0-43, or any other non broken Linux kernel.
  4. Install a non broken kernel: apt install linux-image-4.15.0-43-generic, remove the broken one: apt remove linux-image-4.15.0-44-generic, and reboot.
Please direct any queries to the 1.13.2 discussion thread, or general forums:

EDIT: Please see the below post for updates.