"Vegemite" is an extract of yeast, marketed by Kraft in Australia. Several years ago, a friend brought several jars, correctly guessing that I would enjoy it. When freshly opened, Vegemite can be easily spread on buttered bread. If there's a difference between Marmite and Vegemite, I don't know it. My guess is that the name "Marmite" has been trademarked, but that the extraction process is "in the public domain".
A few years ago, Marmite developed a witty advertising campaign, on the theme "Marmite--you either love it or hate it". I was shown some of the commercials, probably displayed on YouTube. For any readers who don't know about Marmite, it is a sticky brown paste, usually spread on bread, toast, or a plain cracker, with a salty, tangy taste.
As a child, I used to see two brands of meat extract, Oxo and Bovril. As their names imply. these were made from beef . They looked rather similar to their vegetarian cousins, and were mainly used to make "beef tea", a warm drink for cold weather, essentially just the beef extract dissolved in hot water. I seldom saw beef tea, apart from when we were spending days on long sea voyages. On cold nights in later years, keeping watch as a Naval officer, i learned to prefer the strong cocoa we called "Ki", made from dissolved bars of solid chocolate.
The other common usage for Oxo or Bovril was to add flavor and body to soups and stews. In 1951, I learned how these meat extracts were a byproduct of the beef trade between Argentina and the U.K. I took passage in a ship which picked up a cargo of chilled beef in the busy port of La Plata, south of Buenos Aires. A prize-winning article of mine (Meat Boat) about that trade was published in the Spectator later that year.
At our Colorado house, I recently finished my last jar of Vegemite, which had dried up since it was opened many moons ago. I was able to scrape out most of what was left, and even (with difficulty) spread some on an English muffin. Delicious! But there were several lumps that I was able to enjoy, much as I would suck what Brits call a "boiled sweet" and we call "hard candy". I washed out the almost-empty pot and recycled it.
Farewell, Vegemite! Now I can start the little jar of Marmite, awaiting me in the pantry!