Fantasy Grounds is a Windows virtual tabletop application for running real-time RPG sessions over the internet. Out of the box it handles keeping track of the character, inventory, maps, dice rolling, etc. There are other such products but I think FG is the most successful at the moment.
There are presently two versions: FG Classic, which works properly but is dead end, and FG Unity, which is wobbly but the future.
It doesn't include voice, which you're assumed to bring in some other way, most people use Discord.
Add a ruleset, which is a bunch of XML to describe windows and a bunch of Lua to describe behaviour, and it can be customised to a particular system, automated, etc. I'm one of I guess three people who wrote the TFT ruleset, which I feel is finished though it could certainly use some beta testing. Main point of contact is David Edelstein, @Amadan on Discord.
There's an issue with content: legally putting e.g. the weapons table in the code would IIUC be OK. But SJG and I assume SJ personally hate people doing that sort of thing and their web pages utter dire maledictions. So until and unless we convince them otherwise we don't plan on including any of TFT's art, counters, tables, talents, spells, etc. Including some freeware or appropriately licensed counters might partially mitigate the content vacuum.
In case anyone would like to check out the TFT ruleset, for the next couple of days I'll put up a game on the cloud using my latest development version. You'll need a copy of FG Unity (the free "demo" version will do). It should offer you a list of cloud games, one of which will have my name for GM. Unfortunately without a GM logged in you won't really be able to play but you can at least generate a character.