My own with threaded replies and unlimited depth in early 2000 like:
> Thread
>> Re: Thread
>> Re: Thread
Re: Thread
Re: Thread
As it was built into my own MMPORG text based game. Members had no problem with it.
After the game was stable with enough features, I converted it to what you would consider a traditional view (like Xenforo), but with very limited features of title and message with little "emoji" (related to the game) support.
Then I got into blog networks, criminal justice and forex to be exact. The CPC from interlinking was insane for those keywords at the time ($7-25 per click, just incredibly competitive).
But I made my very first mistake opening my first forum in the forex niche on vB3, then vB4, with all the bells and whistles (vB SEO and a ton of brand free DragonByte Tech plugins)...
in a niche I had no interest in and relied on paid content posting — $10,000 sunk, with a saving grace of a $3,000 ad deal right before I planned on pulling the plug; soon as the ad deal played out and they didn't renew, it was shut down. I was down about 50% on the investment, but the blog networks held so it wasn't too bad of a loss when combined.
Anyone want my vB4 license?
Now, I hold several more XF licenses (and will buy anyone's second hand if the price is right), than open forums. But, I'm working on 3 concurrently, about to add the 4th.