How to install latest (untagged) state of a repo using bower?

Specify a git commit SHA instead of a version:

bower install '<git-url>#<git-commit-sha>'

Example:

bower install 'git://github.com/yeoman/stringify-object.git#d2895fb97d'

You can also specify a branch instead of a SHA, but that's generally not recommended unless it's in development and you control all the parts.

Yes, you can point to the git url, or use name/repo shorthand (for github repos):

bower.json

{
  "name": "bower-test",
  "dependencies": {
    "dpm": "[email protected]:okfn/dpm.git",
    "docker-nmpjs": "terinjokes/docker-npmjs"
  }
}

More in the docs

As @roi noted in the comments, you can use the --save flag to automatically add dependencies to bower.json, e.g. bower install terinjokes/docker-npmjs --save