This site features a super-simple premise. TubeReply will play a YouTube video over and over again, until you stop it or go mad — whichever happens first. Just enter the URL of the clip you want repeated and the site will do the rest.

DragonTape allows you to remix YouTube videos into a seamless mixtape. Search for the clips you want, drag and drop to set up the play order and then share the playlist with friends via an auto-generated URL, or embed it with the code provided.

This “mashup helper” exists “because you have better things to do than work.” You can use it to compare two videos, or have fun mashing together two patently unsuitable videos. Simply enter the two URLs, decide on your VJ name, and you’re off and away. You can share your video pairing via a generated URL.

SynchTube allows you to watch synchronized YouTube videos with up to 50 other people with a chat window along the side so you can IM about what’s happening. Setting up a “room” is easy. Just enter the URL(s) of the videos you want to watch and then share the URL with your group. We can imagine tons of uses for this service, but the sweetest one has got to be setting up some videos to watch “together” with a far-away partner.

Enter your choice of keywords into this site and it will create an infinite playlist based on them. Get ready for a seamless viewing experience based on as many keywords as you can imagine.

You can link to a specific spot in a YouTube video by adding #t=MMmSSs (replace MM with minutes and SS with seconds) to the end of the URL, but Spilcd (and TubeChop below) take this concept a step further. Splicd lets you cut down a YouTube video by entering start time and finish time. You can then share your edited clip with a URL or embed it with the code supplied.

TubeChop shares exactly the same principle as Splicd. TubeChop, however, lets you make your edited selection by sliding a bar along a timeline. It’s worth an independent mention as some may prefer TubeChop’s visual editing process.

This unique little tool lets you create a “YouCube,” an interesting, if slightly offbeat way of sharing YouTube videos. Enter the six YouTube videos you want to appear on each side of the cube and it generates a spinning 3D cube of your videos that you can then name and share via a shortened URL.

MixTube is a great, simple tool that lets you easily create and share music playlists from YouTube videos just by adding the URLs to a list. This tool is tidy and useful for songs that you can only find on YouTube, such as mashups, live performances, and other user-generated content.

YouFlow offers an alternative and more attractive way to browse videos on YouTube. Enter your key words and a selection of results will be displayed in a cover flow-style layout that you can scroll through. You can choose to play multiple videos right from the results, something that is much more difficult to do with YouTube’s queues and playlists.

If the majority of YouTube comments depress you, then: a) You’re not alone, and b) There’s a solution. This browser bookmarklet offers a plain white or plain black background to view vids on. Simply install and then hit the “quietube” button after you press play on any YouTube video for some peaceful, troll-free viewing.

TestTube is YouTube’s “ideas incubator,” akin to Gmail Labs, where YouTube engineers and developers “test out recipes and concoctions that aren’t quite fully baked.” You can play around with a comment search, HTML5, the lite version of YouTube (Feather), a caption editor, music discovery features and more.
via mashable