Learning Platforms - Products that are not fully fledged Learning Management Systems (LMS)
SeeSaw
SeeSaw is already in the messaging and feedback categories on this website as it is more than just any one service. It is used world-wide and the free version allows you to do quite a bit. Well worth having a look and seeing if it could help your teaching. NB SeeSaw for schools is the paid version, I think there are some features in the video not available on the free version.
formative
Formative is a very comprehensive platform that you can run on a freemium account. However you are limited, most significantly in the question types that you can create in a quiz. And in the paid version there are a superb selection of different question types. However it is a very complete platform even on freemium.
Nearpod
I heard about Nearpod for the first time around the onset of covid, the timing could not have been better! I didn't end up using it with my classes but several colleagues did and had only good things to say. The ace for Nearpod is the 'live' nature of it and the ability to view your students' work/screens live. If you have 1-to-1 devices, it's definitely a product to be aware of.
Classum
Classum looks like a nice product, just not one that particularly suits subject/field. The video here is for the full paid for version but there is a free version on which you still get a lot of functionality. If you have looked at ParentHub there is a similarity here, as Classum allows you to post notices etc. and also shows you clearly who has read them. A nice feature.
Edublogs
Edublogs is best understood through this video. It is definitely a good platform that could enhance learning for many students. My only thought is the ease of use. If you have some wordpress experience then you will find it a breeze, if you have not had any wordpress experience then you may want to make extensive use of templates.
Edulastic
Edulastic is maybe not quite as complete in terms of the word 'platform' as some of the others here, but it also feels more than just a quiz site. Possibly this is just because Edulastic probably offers the most advanced quiz features I've seen for free online period. You get a vast choice of question types and you can see results LIVE, like literally each question live which is fantastic!