The revived Doctor Who series has produced a number of mini supplemental episodes. Some of them aired as part of TV specials or other TV series, some as bonus DVD features, some for digital television in the U.K. While most of those are probably available online, I wouldn't consider them webisodes. (I'll mention some of them in my TV specials section.) In 2006 there were 13 Tardisodes (which I haven't seen) that were supplements to the series 2 TV episodes, available on mobile phones and on the BBC's website.

There were also online minisode prequels to several episodes of series 6, series 7, series 9, and series 10. (I didn't see any of those when they were first released, but I did watch at least some of them several years later, on Amazon.) I don't really feel like the episode prequels are worth mentioning individually, but there are some other webisodes I do want to mention specifically, as tie-ins to specials or to entire seasons.

Pond Life (on bbc.co.uk and YouTube)
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This is a series of five webisodes, each a minute or so in length, which were released in August 2012, leading up to the premiere of series 7 of Doctor Who. However, I didn't see them until 2018, on Amazon... and I watched them near the end of the first part of series 7, instead of before the season, since that's the date Amazon listed for it. Pff. Amazon. Anyway... the Doctor makes a series of phone calls to Amy and Rory, and occasionally shows up at their house. Mostly it's all just sort of amusing, but the last webisode hints at a problem that would be seen in series 7. Rather dramatic, but... since I'd already seen the outcome, not as troubling to me as it could have been.

P.S. (on bbc.co.uk)
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This was released in October 2012, after the midseason finale of series 7, but I didn't see it until February 2024. It starts with a scene from the end of the episode "The Power of Three", but the bulk of the webisode is a storyboard animatic, in which a man delivers a letter to Rory's father, Brian. We hear Rory read the letter in a voiceover. It explains a bit of what happened to Amy and him, and why Brian would never see them again. It's really quite poignant.

The Snowmen prequels
This is a series of three prequel minisodes to the Christmas special The Snowmen (although the third one was released a few months after the special aired). The first prequel aired on TV in November 2012, as part of the annual Children in Need telethon. But I'm including it in the webisodes section because of its relationship to the other two prequels, which were released online. The first two prequels can be watched either on YouTube or as bonus features on Amazon's Doctor Who Christmas specials page (for the eleventh Doctor), or on iTunes. The third can be watched on Amazon's page for Doctor Who series 7, part 2. Anyway, they're all fairly amusing.

The Great Detective (on BBC 1)
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A Silurian named Madame Vastra is a detective in Victorian London, assisted by her human wife Jenny Flint, and a Sontaran henchman named Strax (collectively known as "the Paternoster Gang"). They had previously been seen in the Doctor Who series six episode "A Good Man Goes to War." They currently want the Doctor's help in an investigation, but he tells them he's retired.

Vastra Investigates (on bbc.co.uk and YouTube)
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The detectives have just wrapped up a case, helping Scotland Yard. Later, Vastra and Jenny notice that it's snowing despite there being no clouds in the sky.

The Battle of Demons Run: Two Days Later (on iTunes and Amazon)
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This is set two days after "A Good Man Goes to War," and sometime prior to the first two prequels. It explains how Strax came to be working with Vastra and Jenny.

The Night of the Doctor (on bbc.co.uk and YouTube)
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This was released on November 14, 2013, but I didn't see it until July 2018. It's part of the lead-up to the 50th anniversary special, The Day of the Doctor. It begins with a woman named Cass, on a spaceship that is about to crash, after the rest of the crew had transported off the ship. The eighth Doctor (Paul McGann, previously only see in a 1996 TV movie) shows up and tries to rescue her. But when she realizes he's a Time Lord, she decides to remain on her ship, as she would rather die than go with him, because the Time War between the Time Lords and Daleks has caused such unspeakable devastation throughout the universe. After the ship crashes on the planet Karn, the Doctor is brought temporarily back to life by the Sisterhood of Karn (previously seen in a episode of the original series). One of the sisters, Ohila, tries to convince the Doctor to drink an elixir that would trigger his regeneration, but allow him to choose the kind of person he would become. After having kept out of the Time War ever since it began, he finally decides that he has to become a warrior, to put a stop to the war. His new form is portrayed by John Hurt (previously seen briefly at the end of the series 7 finale). Well... it's definitely a very dramatic story, for its very short runtime. And it very much whets the appetite to learn more about the incarnation that will come to be known as the "War Doctor" (despite his not wanting to use the name "Doctor" in this incarnation). It's kind of strange for me seeing this five years after it was released, because before this, I had been vaguely aware of the War Doctor, but I kind of had the impression that he had originated in either novels or audio dramas, before appearing in any visual form (either on TV or the web). But in fact, his appearance in books and audio dramas came later. (I've never read or listened to any of them, and I don't know if I ever will.)

The Last Day (on bbc.co.uk and YouTube)
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This was released on November 21, 2013, but I didn't see it until July 2018. It's another lead-up to "The Day of the Doctor." It's set on Gallifrey during the Time War, and we see through the eyes of a new recruit who has just been implanted with scanners or something. Another soldier is explaining things to him, but this is frequently interrupted by glitches that apparently some people believe are premonitions, but which the soldier tells the recruit are just hallucinations, a side effect of the process. The recruit is then taken to meet another soldier, who will explain his task of monitoring for any Daleks that might attack, which is supposed to be impossible. Anyway, we never really see the recruit himself, nor does he say anything. But... the whole thing is rather horrific.