From a project and community management standpoint TMK maintains all the officially supported keyboards by himself, with a bit of community support. Separate community maintained forks exist or can be created for other keyboards. Only a few keymaps are provided by default, so users typically don't share keymaps with each other. QMK encourages sharing of both keyboards and keymaps through a centrally managed repository, accepting all pull requests that follow the quality standards. These are mostly community maintained, but the QMK team also helps when necessary.
Both approaches have their merits and their drawbacks, and code flows freely between TMK and QMK when it makes sense.
From a project and community management standpoint TMK maintains all the officially supported keyboards by himself, with a bit of community support. Separate community maintained forks exist or can be created for other keyboards. Only a few keymaps are provided by default, so users typically don't share keymaps with each other. QMK encourages sharing of both keyboards and keymaps through a centrally managed repository, accepting all pull requests that follow the quality standards. These are mostly community maintained, but the QMK team also helps when necessary.
Both approaches have their merits and their drawbacks, and code flows freely between TMK and QMK when it makes sense.