See also 'Core/Combined' for some websites that cover more than just Maths and are not listed separately here.
Maths Kitchen
Maths Kitchen is a great website for students, particularly at home and there is a significant free section.
SplashLearn
SplashLearn is for reception -Yr6. It is a platform full of games with a dashboard for teachers to track and monitor. It is as free as I can tell...
99MATH
99Math is a totally free short quiz website, a bit like Kahoot, but just for Maths. However, all the quizzes are already made! You just customise them :-)
Blutick
Blutick is a very complete package I would recommend every maths teacher take a quick look at, they are also trying to offer as much as possible for free, which is a lot!
DrFrostMaths
DrFrostMaths has been around for a long time and has always stuck to the aim of keeping things free. Another very complete platform worth your time investigating.
Diagnostic Questions
Diagnostic Questions is another complete Maths platform and you can do most things for free. I would only add that of the similar products around I find diagnostic questions one of the harder websites to navigate.
Mathigon
Mathigon is very 'student-led'. Many of their activities are well worth looking at, my personal favourite is the timeline of mathematics.
ASSISTments
ASSISTments looks like a great product, however for anyone UK based, it is very USA aligned. I've therefore found it quite difficult to explore as the curriculums are not what I expect or have experience in.
GeoGebra
GeoGebra has developed a lot since I became a teacher. It is now full of engaging activities that you can even assign to classes and view progress in real time.
Desmos
Desmos is a well known free graphing tool, however you can also create all sorts of quizzes in desmos and run live assignments. You can do a vast amount for free, however it is not the simplest platform to navigate.
Websites
Maths Genie
Maths Genie is already very well known. It houses a plethora of questions across GCSE, A-Level and KS2. Within GCSE you can get topic booklets + solutions or past papers for 3 major exam boards.
MathsBot
MathsBot is a brilliant website with an enormous array of Maths tools. If you are looking for a tool to help your explanation, MathBot probably has it! I also find the grade boundary page very useful.
Resourceaholic
Resourceaholic is a legendary website run by @mathsjem It is super useful for finding resources when planning.
Corbettmaths
I first got onto corbettmaths through his YouTube videos. I often found them the best explanations of topics. It has since been expanded to worksheets, the 5-a-day and more.
IXL
IXL is a website many will know. If you want to be a member it will cost, but just to view the resources is free, and they have every topic covered from reception to Year 13!
BBC Bitesize
BBC Bitesize surely needs no introduction. Obviously it covers more subjects than just Maths, but here as a reminder that Maths is in the list!
Mathsisfun
Mathsisfun is often high on the google search when you ask a maths question, and the reason is they give great explanations and examples. Simple as that I think.
A+ Click Maths
A+ Click Maths is about helping nuture problem solving students. Pick a topic or a level and start answering questions, the programme always suggests another question.
Math-Aids
Really useful website for making worksheets that I have used plenty in the past, it does have a slightly over-active ad-blocker warning though.
ExamSolutions
I owe something to ExamSolutions as I remember it being instrumental in much of my own A Level Maths learning. It has since expanded and now has a whole platform, but the videos are still free :-)
Arithmetic Game
Just straight forward arithmetic practice. It's easy, it works and it's quite addictive.
that quiz
I owe something to ExamSolutions as I remember it being instrumental in much of my own A Level Maths learning. It has since expanded and now has a whole platform, but the videos are still free :-)
NRich
UK Maths teachers are bound to know about NRich and its extensive library of resources already. NRich is well known for activities that really deepen students' thinking, 'enriching' their experience.
White Rose Maths
White Rose Maths does have some paid for areas but there is more than enough free to warrant its place here. I particularly like the downloadable pdf 'End of Block Assessments'.
Miss B's Resources
Miss B's Resources is a personal favourite. They featured heavily in my early teaching and I always thought her worksheets were well designed.
MacTutor
An extraordinary collection of mathematical history. I am sure all Maths teachers would like to be able to spend more time looking through some of these biographies.
PixiMaths
PixiMaths is another personal favourite. I regularly used these PPoints and resources in my early teaching. With more resources regularly added, I would add to your list to check out.
MathsWhiteboard.com
Matt who runs MathsWhiteboard appears to have endless ideas and the ability to put them into practice. There are a number of tools on his website that could be worth discovering.
Transum
Transum is a gold mine for Maths questions, I particularly like their levelled activities, they are excellent for independent practice.
Apps
Desmos graph
If you want to plot something, anything, this is the app for it, no questions.
Desmos Scientific
Not content with just superb graphing, Desmos went and made an awesome calculator too!
Photomath
Photomath can solve equations, pretty much any equation, just point your camera at it. Now you might be getting worried about cheating... but photomath shows the steps, so maybe it could actually help?
Panecal
I found Panecal a few years ago when looking for an app that would simulate your normal looking Scientific calculator. I still use it all the time.