Overview
Castle VTT is currently in active development, so features discussed or shown in screenshots may change.
Castle VTT is a virtual tabletop that runs on the GM's own computer. The desktop app contains the whole server, so there is nothing to rent and nothing to configure. One click puts the table online through a Cloudflare Tunnel, and players join from a browser link. There are no seats to buy and no per-player cost, and the campaign lives on the GM's disk as a database file and an uploads folder they can copy or back up like any other folder.
It ships its rules engines in the box rather than assembling them from modules.
Pathfinder 2e 
https://groupfinder.gg/library/pathfinder-2nd-edition-2019 Remaster enforces the three-action economy, the multiple attack penalty and four degrees of success;
D&D 5e https://groupfinder.gg/library/dungeons-dragons-5e-2014 handles true multiclassing with a shared slot table, separate Pact Magic and per-class save DCs. Both share dynamic lighting with walls and doors, per-player fog of war, server-rolled dice, a 1-20 character builder, and peer-to-peer voice between players' browsers. Importers cover Foundry, Roll20 and Universal VTT, plus a PDF-to-compendium tool with a review step.
Castle VTT is in open alpha. Windows, Linux and macOS.
Links
castlevtt.com https://castlevtt.com/ - Official website