Great graduate courses that went online recently In 09.2020 by pure chance I discovered the YouTube channel of Richard Borcherds where he gives graduate courses in Group Theory, Algebraic Geometry, Schemes, Commutative Algebra, Galois Theory, Lie Groups, and Modular forms! (and an undergraduate courses in Theory of numbers and Complex analysis).
I watched so far about 300 of his videos (about 90%) and they are really great. Borcherds is an amazingly good lecturer (for my taste). It is also clear, that these lectures were worked out/improved through years, since Borcherds was giving similar ones in Berkeley (one can find some lecture notes by students online). I would guess, that currently there are some other great lecturers that started to upload their courses on YouTube (or some other platforms). For this reason a question.
Question. If you watched recently an online graduate course (free for all), and found it brilliant, by a lecturer whom you find great, and believe that the course taught you something, could you please share  the info about it.
The motivation for this question is to spread information about exciting things happening in mathematical life/education lately.
 A: Discrete Differential Geometry
Keenan Crane, Carnegie Mellon University, Spring 2021.

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A: Over the last term Jarod Alper has taught a course Introduction to stacks and moduli, introducing algebraic spaces and stacks and with the goal of proving (or outlining) properties of the stack $\mathcal M_g$ of curves, its compactification and their coarse moduli spaces. The recordings of the lectures are available and a pretty complete set of notes has been compiled.
The course only assumes prior familiarity with standard scheme theory, however a lot of other background material is covered in the appendices. One warning is that Jarod uses a bit of nonstandard terminology regarding stacks in general.
A: Two more recent ones (I think they are both still going on):

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*Topological Manifolds


*Surgery Theory
A: The lectures for Steven Strogatz's (ongoing) course on "Asymptotics and Perturbation Methods" are posted to his YouTube channel: https://www.youtube.com/user/stevenstrogatz1/videos. Strogatz is an outstanding lecturer.
A: Algebraic Geometry in the Time of COVID (AGITTOC) happened during late summer of 2020. Ravi Vakil gave what he called "pseudolectures" following his "Rising Sea Notes". He didn't cover the whole book.
Link to the pseudolectures
The blogposts, for some guidance through the exercises, and other thoughts:
He was planning on starting it up again in some capacity, at some point, but I don't know what happened to that plan. This gave some structure and purpose to what was otherwise a miserable and depressing summer for me, so I have a soft spot for it.
A: Here we go again.

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*Integration Theory by Professor Marcus Carlssons, link: https://youtu.be/EzoaGgBHJEQ


*Graduate Real Analysis by Professor Emanuel Carneiro, link: https://youtube.com/playlist?list=PLp0hSY2uBeP8hajKOVGZ9oIPjG3HKMfoY


*Graduate course on “Groups and Galois Theory” by Professor Yuly Billig, link: https://youtube.com/playlist?list=PLu6jbin1VpDBGWvctA_vGFLXzJD8YsA3F


*Differential topology course at IMPA by Professor Vinicius Ramos, link: https://youtu.be/yOoWugX1AOI


*Introduction to Algebraic K-Theory, link: https://youtube.com/channel/UCNefIuLog1bTwR0rav3p_5A


*https://youtube.com/c/UndergraduateMathematics YouTube channel is crazy. Just check out entire playlist of that channel. That channel is a window to thousand different graduate level math courses.


*Introduction to Stacks and Moduli by Professor Jarod Alper, link: https://youtube.com/playlist?list=PLhFI5R_xInjdhtWuhgYlA8NZGXO-unnl4


*Higher Algebra, link: https://youtube.com/playlist?list=PLsmqTkj4MGTDenpj574aSvIRBROwCugoB. Topological Cyclic Homology, link: https://youtube.com/playlist?list=PLsmqTkj4MGTB8pNGvW0iuKUFmBlOSke-C


*SubRiemannian geometry course by Professor Enricole Le Donne, link: https://youtube.com/playlist?list=PLleGBpoKCrJn21-tCrNRk6JAyh4gwtgks


*Area formula-Geometric Measure Theory, link: https://youtube.com/playlist?list=PL_c66HM3gCshuMPW7BgVdWg_I8OitI7mC


*Category Theory by Professor Ivo De Los Santos Vekemans, link: https://youtube.com/playlist?list=PLHYBb0FtzAK9TBFhZ8eZzJRc5gW1NNp2K


*Algebraic Geometry, link: https://youtube.com/c/AntonMosunov


*Stanford Algebraic Geometry Seminar, link: https://youtube.com/playlist?list=PLdBhxg1X10QTkMv9XKj7h0naLhwKY-qw_
A: Most of them are not so recent as you are asking for, but in my opinion is still worthy to look at them.

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*Claudio Arezzo's lectures on differential geometry
https://www.youtube.com/playlist?list=PLp0hSY2uBeP_2dottSdX0eLPV_but7UAG


*All the videos of Joe Harris are wonderful in my opinion, see: https://www.youtube.com/playlist?list=PLTWOVL6OX7hCIFAbbE4q0aSCrRv4aUxax, the Eilenberg lectures: https://www.youtube.com/playlist?list=PLj6jTBBj-5B_QE35IEQgLkkEct0Dk8GG6, the lectures on Poncelet's theorem https://www.youtube.com/watch?v=P7E_YOiuDvI


*Robin Hartshorne's lectures on deformation theory: https://www.youtube.com/playlist?list=PLTWOVL6OX7hC2KrBaxkx_dzEpHyOJqMZm


*All the lectures on Algebraic Geometry by Miles Reid, even if the audio/video quality is not the best. See for example: https://www.youtube.com/playlist?list=PLY28_CByrwHZ0UOqfuw6KVgKIE6-Go0RG


*Pierre Albin's series on algebraic topology: https://www.youtube.com/playlist?list=PLpRLWqLFLVTCL15U6N3o35g4uhMSBVA2b


*The channel of Federico Ardila for the lovers of combinatorics: https://www.youtube.com/user/federicoelmatematico/playlists


*These lectures by Bernd Sturmfels on tropical geometry: https://www.youtube.com/playlist?list=PLRy_Pn1LtSpfYE39TuCZrJAi7-0z44sQB


*Andrew Snowden's channel: https://www.youtube.com/channel/UC5f0ii9uewnsgu0WuyNkfLQ/videos


*Do not forget Norman J Wildberger's channel: https://www.youtube.com/user/njwildberger, it is very good, even if he thinks that infinity does not exist :)


*Finally since I've fallen in love with Don Zagier, I suggest all of his lectures on youtube. If I had to advise a particular one, certainly the series at ICTP "Rogers-Ramanujan identities and the icosahedron" https://www.youtube.com/playlist?list=PLLq_gUfXAnkn64UkHxrM9wWZnBXy6xUM7
Let me finish citing some maybe less technical channels but still very enjoyable.

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*The Math doctor Bob series on Representation Theory: https://www.youtube.com/playlist?list=PL57457844458A5A1F

*Billy Woods's channel on algebraic number theory: https://www.youtube.com/channel/UCcNQgs6bKds_KBpjp2_oavw/videos

*If you love competition maths problems with also some insight in analysis Michael Penn's channel is a must https://www.youtube.com/channel/UC6jM0RFkr4eSkzT5Gx0HOAw
A: Yufei Zhao has a course titled "Graph Theory and Additive Combinatorics" available on MIT OpenCourseWare.

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*YouTube link to lectures

*Link to full course materials
A: Here’s a course on C*-algebras and compact quantum groups by in my opinion a genius lecturer https://youtube.com/playlist?list=PLq3E5oubNNoAZi6W7968tNkSnIGTt4hEn
He also has a  course on functional analysis (see the HSE youtube channel where the above lectures are uploaded). It is different from the most because he takes more algebraic approach.
A: This course on Real Algebraic Geometry from Konstanz Universität's professor Markus Schweighofer is a really good introduction to the topic.
A: Timothy Gowers on combinatorics.
YouTube link: Topics in Combinatorics
Sean Prendiville on additive combinatorics. His lecture is somewhat scattered on the webinar page. He also provides lecture notes.
YouTube link: Fourier Methods in Combinatorial Number Theory
A: Frederic Schuller, theoretical physics, brilliant lecturer:

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*Lectures on the Geometric Anatomy of Theoretical Physics

*Lectures on Quantum Theory

*The WE-Heraeus International Winter School on Gravity and Light
Not pure mathematics, I know, but brilliant introductions to some very advanced applications.
A: IMPA has several courses online, some of them in English, including:

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*Master Program: Probability Theory

*Doctorate program: Functional Analysis 
You can find all courses (including those in Portuguese) here.
A: I think Dev. Sinha's channel also is a great source for people interested in algebraic topology.
A: Carl Bender's lectures on very powerful but non-rigorous perturbation theory methods used in theoretical physics.
A: Ben Webster gave an introductory symplectic geometry course this past term which I think was very good. The presentation was pretty elementary. The course was offered through the Fields Institute, and their YouTube channel also has links to some other courses by some professors around Ontario which were offered in the same way.
A: Course on Metric Space by Professor Ben Green https://youtube.com/playlist?list=PL4d5ZtfQonW10k_fkbX-9Jj7HGAqRZbM3
A: I have recently discovered this YouTube channel https://youtube.com/channel/UC-ssgSLLaFYn1LARgEAqWBg which contains lots of mathematical physics and mathematics course.
1)Introduction to topological field theory, link: https://youtube.com/playlist?list=PLqX5gFCSJtMC7tju8pAoZZ_RqYeXoEYxl
2)Quantum Mechanics for Mathematicians, link: https://youtube.com/playlist?list=PLqX5gFCSJtMBA62lNda_l5jRV09LklQ0s
3)Quantum Information Theory, link: https://youtube.com/playlist?list=PLqX5gFCSJtMBA62lNda_l5jRV09LklQ0s
Also explore the whole playlist created by this channel. I hope you will find something useful.
