CalledItMate lets you start a private prediction league and invite whoever you want with a single link. Your group gets its own table, and everyone competes on the same matches - predict the correct score before kick-off, then call goalscorers and the next team to score while the game is live. Points land the second the match proves you right, so the table moves during the game rather than the following morning.
It is free, there is no entry fee and there is nothing to stake. That makes it work for an office league or a group chat where a betting app would be a non-starter. Create a league, share the invite link, and everyone who joins is in your private table. You can be in as many leagues as you like at once, and everyone is still ranked on the global seasonal leaderboard, where the winners win real cash.