+10. I think this question has the potential to become a great resource not just for you but for a lot of future visitors as well! I simplified the title, and commented out the last paragraph because we actually had a question about bannedbygaussian.org before, which got closed, but perhaps could be resurrected if it's done in the right way. By the way, we have a GAUSSIAN chat room, where you can ventilate further grievances against GAUSSIAN beyond what would be appropriate in a question on the Main site :) — Nike Dattani 22 hours ago

I think this question could be improved with a little more detail. As is, the answer is basically this list minus Gaussian. It would help if you stated explicitly your criteria for a suitable replacement. Does it have to be free/open source? Do you want to be able to benchmark or avoid some specific licensing terms? Is there some specific features/methods you need? — Tyberius ♦ 8 hours ago

Even ignoring Gaussian's business practices, scientists should choose open source codes as much as possible for transparency and reproducibility. Furthermore, we need to encourage funding agencies to support code development and user support. — WaterMolecule 7 hours ago

@Tyberius That list contains plenty of solid-state and molecular-dynamics software that have essentially zero overlap with GAUSSIAN, plus the list doesn't go into nearly the level of detail as some of the answers below, and there's not much space to comment or vote. Even some Wikipedians agree that Wikipedia is not a replacement for StackExchange. The question had the open-source tag, but is open to closed-source suggestions too. I think all software except Gaussian allow benchmarking? Listing features/methods needed — Nike Dattani 6 hours ago

could certainly have helped make this a more focused question but it's a bit too late for that, since if the user lists some feature which is unique to GAUSSIAN, all answers below will have to be deleted. I think the topic of this question and its answers raises a lot of discussion points for sure, and I'd be happy to chat more in the GAUSSIAN chat room if this comment chain becomes large (this is an HNQ after all). — Nike Dattani 6 hours ago

@NikeDattani I know there are some that wouldn't apply. My point is that if we are going to have a big list question that is essentially "give a brief description of any/every quantum chemistry program besides Gaussian" it probably make a better general reference question to just have "give a brief description of any/every quantum chemistry program". Otherwise, we could in principle get a bunch of "what is a good replacement for GAMESS/MOLCAS/etc" questions where the only difference is which program is excluded. — Tyberius ♦ 50 mins ago

@Tyberius This comment chain is becoming long for a question with 1000+ views (and still counting), I suggest we wipe out the comments and move this discussion to chat. — Nike Dattani 37 secs ago