I have created a new space in the organisation and I have to move several apps from one space to the newly created one. How can I do this? (I don't want to rename the old space since only a subset of its apps need to be moved.

I'm afraid there is no such function to move apps from one space to another. There are two possibilities to achieve it, though:

Compile & Push

If you have access to the source-code of the app and use a common CI/CD setup, simply adjust your scripts, have them point to the new space and trigger a complete CI/CD cycle.

Download & Push

If you don't have access to the source-code, the binary-repository where you store your binaries or have to ensure it is 100% the same droplet in the new space, you can download that droplet from Cloud Foundry and push it to the new space:

1. cf app source-app --guid to get your source app guid
2. cf curl /v2/apps/:source-guid/droplet/download --output /tmp/droplet.tgz to download the source app's droplet to your local machine (note that if your Cloud Controller is configured to use a remote blobstore this command will return a redirect to the actual location of the droplet)
3. cf target -s destination-space to target the space you want to push the copied droplet to
4. cf push --droplet /tmp/droplet.tgz destination-app-name

Credits: Github

This will work for buildpack-based apps but not for Docker-based apps, as you can't simply download docker-binaries.

Pitfall: If you want to use the same route again, don't forget to delete (not just unbind) it from your old space.