Can I create my own 'fund' of sorts to auto-allocate across several stocks?

Sorry if this is a pretty basic question, but I'm rather new to buying stocks myself.

I'm trying to purchase stocks in an industry I'm very familiar with and want to diversify across several companies in that industry. I'd like to allocate some amount of money evenly across them on a repeating basis. I'd also like to be able to add other companies down the road and have it automatically divvy up the money accordingly as I add.

I had this thought and then realized that's essentially what an index fund is, right? For every dollar you input, it gets allocated across multiple companies in fractional shares. I was wondering if I could do the same thing for myself.