I see. Vanguard Total market fund tracks CRSP US Total Market Index, which requires 15 million market cap min - I guess OTC stocks are included if they meet this requirement. I didn't realize that OTC were included in that fund, thought it was only listed, starting with micro caps.Yes, Vanguard allows free OTC and penny stock trading, except for certain OTC stocks that are on the "gray list" or something like that. Also, OTC stocks that are not available through the US-based exchanges get a $50 "overseas stock" fee, even though one of the companies I tried to buy, Titan Mining, is a Canadian company. I'd say about half of the OTC stocks, mentioned in this thread, were on Vanguard's banned list.
Otherwise, Vanguard is very easy to use. I buy/trade the stocks within my Roth IRA account so I won't get a capital gains tax when I sell them. Although, at the amounts I'm buying (less than $1000 total), there probably wouldn't be much capital gains taxes unless any of those stocks really shoot through the roof on price.
With Vanguard, you can get exposure to most non-penny small and mid-sized company stocks (like Palantir) through one of their funds or ETFs. Palantir, for example, is part of the portfolio in their mid-cap funds and ETFs, a couple of which I have money in. So, I'm using Vanguard's brokerage for penny stocks because those stocks (some of them) are only included in Vanguard's Total Stock Market Index Fund, which dilutes the advantages you would potentially gain with careful stock picking.