Docker Related

canister.io — 20 free private repositories for developers, 30 free private repositories for teams to build and store Docker images
Container Registry Service - Harbor based Container Management Solution. The free tier offers 1 GB of storage for private repositories.
Docker Hub — One free private repository and unlimited public repositories to build and store Docker images
Play with Docker — A simple, interactive, fun playground to learn Docker.
quay.io — Build and store container images with unlimited free public repositories
ttl.sh - Anonymous & ephemeral Docker image registry