I've had a male betta (Siamese fighting fish) with male and female guppies and platies. It REALLY depends on the attitude of your male betta. I have one or two that would do fine in a community tank (in fact, Tristan, the one in my 55gal, is a young male and he gets on fine with everyone, even the female bettas...but he's young). I have quite a few (Edward, Alec, Dragon, Emmett, and Amun, to name a few) who I wouldn't even trust with a snail...although Emmett has done well with his two otos. Also, I would trust mollies with a male betta. The mollies can be a bit aggressive with slower-moving fish like bettas (from what I've read and heard). IDK. If you can find a laid-back betta, I'd say go for it if you have the room. Just have a smaller (~5gal) tank available in case the betta doesn't work.