groups.el

(defvar current-group nil)

(defvar groups ())

(defvar buffer-list-snapshot (buffer-list))

(defun switch-group (group)
  (interactive (list (completing-read "Group: " (mapcar #'car groups))))
  (setq current-group group))

(defun create-group (group)
  (interactive "sName: ")
  (if (assoc group groups)
      (error "Group already exists.")
    (switch-group group)
    (push (list group) groups)))

(defun group-new-buffers ()
  (when (assoc current-group groups)
    (dolist (buffer (set-difference (buffer-list) buffer-list-snapshot))
      (push buffer (cdr (assoc current-group groups)))))
  (setq buffer-list-snapshot (buffer-list)))

(add-hook 'buffer-list-update-hook #'group-new-buffers)

(defun kill-group (group)
  (interactive (list (completing-read "Group: " (mapcar #'car groups))))
  (mapc #'kill-buffer (cdr (assoc group groups)))
  (setq groups (remove* group groups :test #'equal :key #'car)))