Is it possible to somehow run Bukkit on singleplayer Minecraft?

There is:

Step 1: Download bukkit https://getbukkit.org and rename the file to bukkit.jar

Step 2: Make a folder at your desired location and name it whatever you want

Step 3: Copy the jar to your server folder you just created

Step 4: Open cmd or terminal depending on your OS and do

cd yourFolder/Directory

java -Xms2G -Xmx2G -jar bukkit.jar

You can replace the 2G with 4G or 1G basically the amount of RAM you wanna use

Step 5: Now if you open the folder you should see that there are some new files created if you did everything right

Step 6: Open eula.txt and change the 'false' value to 'true'

Step 7: Open server.properties and set the server-ip to localhost or 127.0.0.1 which will run the server on your own computer

Step 8: Go to your terminal or cmd and type stop

Step 9: Type java -Xms2G -Xmx2G -jar bukkit.jar again or create a bat file for easier access

Step 10: Now the server will actually start and you should see the plugin folders and other server folders created now you need to put the plugins you wanna use in it

Step 11: Now go to Minecraft then direct connect and type the ip 'localhost' or 127.0.0.1 and there you go you're gonna join the world like a single player only on your computer. The only downside is that you can't pause the game.

Now whenever you wanna play just do that command in terminal

HOPE IT HELPS