Push only part of git repository to second remote repository

I have an existing git repository (e.g. in my organisation's private repository) consisting of several sub-projects organised in specific folders. It there a way to clone each of these sub-projects to specific second remote repositories (e.g. on github)? I'm aware of git subtrees which seems to be convenient the other way around (having existing subprojects as dependencies in a new overall project). However, using subtree would require me to remove the sub-projects from the existing overall project and add them as subtrees again, if I understand correctly.

A requirement is to be able to push the entire project including its sub-projects to the private organisation's remote repository, to achieve a working version there.

Solution

Have you read the subtree docs?

  split [<local-commit>]
      Extract a new, synthetic project history from the history of the <prefix> subtree of <local-commit>,
      or of HEAD if no <local-commit> is given. The new history includes only the commits (including
      merges) that affected <prefix>, and each of those commits now  has the contents of <prefix> at the
      root of the project instead of in a subdirectory. Thus, the newly created history is suitable for
      export as a separate git repository.

Sounds like what you want.

Here's a worked example;

Init a demo repo;

mkdir subtree-split
cd subtree-split/
git init
git commit -m "Init." --allow-empty

Add some content for project A;

mkdir A
touch A/README.txt
git add A/
git commit -m "Readme for A."

Add some content for project B;

mkdir B
touch B/README.txt
git add B/
git commit -m "Readme for B."

Split off B as a new subtree;

git subtree --prefix=B/ split

Make a new repository to push just the history of B to;

cd ..
mkdir subtree-B
cd subtree-B
git init
git commit -m "Init subtree-B." --allow-empty

Push the subtree B history to the remote;

cd ../subtree-split/
git subtree --prefix B/ push ../subtree-B HEAD

Check the history of B;

cd ../subtree-B
git log --all  --pretty=oneline --abbrev-commit
a26e5de (HEAD -> master) Init subtree-B.
0523c62 (HEAD) Readme for B.

No history of A!