In a pot over medium heat, combine beef ribs and water. Bring to a boil, skimming scum that floats on top.
When the broth has cleared, add onions, tomatoes, and fish sauce.
Lower heat, cover and cook for about 1 1/2 to 2 hours or until meat is fork-tender.
Add gabi and cook for about 6 to 8 minutes or until soft.
Add chili and radish. Continue to simmer for about 2 to 3 minutes.
Trim about 2 inches from the kangkong stalks and discard. Cut kangkong into 3-inch lengths, separating the sturdier stalks from the leaves.
If using packaged tamarind base, add into the pot and stir until completely dissolved. Season with salt and pepper to taste.
Add kangkong and continue to cook for about 1 minute. Serve hot.