I'm sure you mean that some or all of your light switch boxes were wired without a neutral connection in the box? A neutral is not required for a light switch, and that is allowed by code. In that's the case, then you can't install any powered electronic device like a smart switch in the box without running a new power line because it can't draw power from your household AC without a neutral connection.
An alternative is to use smart bulbs, since they are powered as long as you leave the light switch always on. If you just want to try one or two smart bulbs to see what you could do with smart lighting, the TP-Link WiFi bulbs are on sale at BB right now, and they don't require a hub or any other accessories beyond household WiFi. But it you get into smart bulbs in a bigger way, it would be better to go with a system like Phillips Hue. Costs more up-front for the hub, but the bulbs are cheaper.
As for a smart switch/dimmer working without a neutral wire, it can't. Any electronic device needs power to operate. These devices get power from your household AC in the box where they are installed. You only get AC power by connecting to a hot lead and a neutral lead (connecting to ground would be a ground fault, a big No-No that wouldn't work properly). When you have just 2 wires in a switch box, the correct code connection is that the switch is interrupting the hot lead to the light, which in turn has a neutral connection on the other side. In theory you could draw power across those two leads, but only by running power through the light bulb even when it's off. That would only work with an incandescent light bulb, and it would cause the light bulb to light up dimly when it's supposed to be off. In any case it's not allowed by code.