Personally, I so far invested 1.5 years into trading, collecting unique data, testing ideas, etc. So far, I came up with only a couple of profitable bots. Here's a very remote hint of what they do:
Horses pre-off trade
Based on certain market metrics, it lays a horse X minutes before the off, then closes the trade at scheduled off time. It does around 10 trades per month: some win, some lose. Given a trading stake of £100, it makes a profit of £20-60 every month. Here's the thing: I tested this for 12 months with £2 stakes. It performed really well every month with the exception of Jun-Aug. Only last month, after a year of testing, I was confident enough to raise stakes. Going well so far.
Greyhound value betting
Based on certain market metrics, it backs a greyhound to win the race. It places 200+ bets every month. If you bet £1 per dog, you can expect at the end of the month to be up £10-20. Bear in mind that almost every month at some point this strategy finds itself down £10+ because of losing streaks. What matters is the bottom line after hundreds of bets at the end of the month. Again, this has been profitable every single month since May (when my data recording began) but only in the last couple of months I felt confident enough to raise the stakes.