My understanding is those are services various government departments can make use of. Notify being to send notifications to people, Pay to take payments, etc.

My understanding is those are services various government departments can make use of. Notify being to send notifications to people, Pay to take payments, etc. These are basically SaaS offerings from GDS to over government departments. The GOV.UK PaaS is a hosting platform for other government departments to host their own software in the GOV.UK managed platform (like a Heroku kind of thing). They're investing more in their SaaS services (Notify, Pay, Forms, Prototyping Kit, etc) and deprecating their PaaS offering in favour of Kubernetes, which looks like it may be offered as a managed service for government departments to use. It reads to me like more of a v2 of the PaaS but it'll now be kube based rather than whatever homegrown thing it is at the moment. Edit: as tnwhitwell pointed out below, the PaaS being deprecated uses CloudFoundry and isn't homegrown.