Foundry is the best fit I've found for the things I want to do. At the time I started looking for a VTT to run my own campaigns & one-shots with, I'd been playing several regular games (5e and Mighty Protectors) on R20 and working on a revamp of the available character sheet for MP.... but I admit I'd built up just a little anger toward R20 for charging me for the privilege of voluntarily improving one of their supported systems.
I spent a little time starting to learn the GM side of R20 but decided to try out Foundry and FGU at the same time, with some specifics in mind:
So I was left comparing Roll20 and Foundry. At the time, though there were a small number of things I thought R20 did better (the process of rolling attack and damage in the default 5e system was clunky and not very configurable - but easily fixed with available mods; the initial sizing/positioning of maps was easier in R20; and why doesn't the core system allow me to long-click a spot on the map to have a marker show up there to draw the players' attention?), Foundry's feature set was just leaps and bounds ahead of what Roll20 offered in terms of lighting, fog of war, audio, etc., and running it at home offered far better performance than I was seeing while playing Roll20 games (this was in the early part of Coronapalooza when R20 was experiencing a lot of growth and lag spikes were common).
In general I just found it more pleasant to work with, and every single Roll20 DM/GM who's played in an adventure on my FVTT setup has made the move themselves. (Okay, it's two people total... but that's still every one of them!
)
(Hopefully I'm not coming across as vehemently anti-R20... it's certainly a viable system that meets many people's needs just fine, for free in many cases, with support for a large number of systems and with a big marketplace full of supporting products.)
I spent a little time starting to learn the GM side of R20 but decided to try out Foundry and FGU at the same time, with some specifics in mind:
- I had no prior investment in digital content on any platform, and being able to purchase official & supplementary content wasn't really a factor. My plan was to run a homebrew 5e setting with a mix of custom encounters and moderately-to-heavily-modified, grafted-in adventures from other sources, and I was willing to put in the time adding non-SRD items on an as-needed basis. (I've since bought a few D&D Beyond products for sheer convenience and used the DDB importer to bring them in.)
- I still wanted to work on an MP system better than the R20 one. No such system existed yet in Foundry but I did discover that Foundry has far more flexibility in system design than R20.
- I'm a tinkerer at heart and liked the idea of being able to modify how things work with some Javascript (without having to pay extra for access to do so).
So I was left comparing Roll20 and Foundry. At the time, though there were a small number of things I thought R20 did better (the process of rolling attack and damage in the default 5e system was clunky and not very configurable - but easily fixed with available mods; the initial sizing/positioning of maps was easier in R20; and why doesn't the core system allow me to long-click a spot on the map to have a marker show up there to draw the players' attention?), Foundry's feature set was just leaps and bounds ahead of what Roll20 offered in terms of lighting, fog of war, audio, etc., and running it at home offered far better performance than I was seeing while playing Roll20 games (this was in the early part of Coronapalooza when R20 was experiencing a lot of growth and lag spikes were common).
In general I just found it more pleasant to work with, and every single Roll20 DM/GM who's played in an adventure on my FVTT setup has made the move themselves. (Okay, it's two people total... but that's still every one of them!

(Hopefully I'm not coming across as vehemently anti-R20... it's certainly a viable system that meets many people's needs just fine, for free in many cases, with support for a large number of systems and with a big marketplace full of supporting products.)