There are some MOOCS which are available for Computer Science GCSE and some MOOCs for Computer Science overall but with a focus on further education.
GCSE:
Provided by the exam board, but has not been updated for the new specs (It is for the course to be taught in 2017)
https://courses.exa.foundation/
This is a "freemium" service with some materials provided for free (first 13 units) but with a paid for service to access all of the materials
Designed to support the teaching of OCR J276 GCSE (9-1) Computer Science. Contains learning resources and assessment resources for teachers to plan and assess the impact on learning.
https://computationalthinkingcourse.withgoogle.com/
This site is provided by Google as part of their vision to bring computational thinking into every subject across the curriculum.
It is well designed with plenty of school based examples to use.
https://learning.thetechpartnership.com/
This site is aimed at Computer Science in general - not specific to KS4 but worthy of a mention because a number of companies have shared their own resources/specialisms. Therefore these are very relevant to real life if not clearly mapped to the KS4 Computing Curriculum.
https://www.class-central.com/subject/cs
Aimed at degree level. This lists all the courses that are currently starting or are open ended allowing the user to select and sign up for a format which works for them. Courses are ranked and rated so the user can measure the impact of courses.