software - Resources for learning Chemistry

Based on various other Stack exchange site (Mandarin Chinese, Russian and German), we adapt this project here for chemistry, since it's a great idea to have all kinds of resources in one place.

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This is a specifically created Community Wiki which gathers resources for learning Chemistry. The lists are a community maintained project, hence everybody with more than 100 reputation points can contribute edits to the appropriate sections. If you feel something is missing, just fill it in. To avoid multiple answers for similar branches, we decided on a general outline, which is locked, i.e. no new answers can be added.
If you have concerns or questions, you can discuss this list on its parent meta post. If they are of a more general concern, you can also post a new question on chemistry.meta.se. This procedure is used, so the comment section here does not become too overcrowded. If you do choose the second option, please leave the link to it in the comments to this post.

Organization

• Answers have a type of resource each.


• If possible, state whether the material is directed towards a beginner, intermediate or an advanced audience.



• Do not include links that lead to illegal content or sites that host such content. If you see any, please flag for moderator attention and choose "other" so you can point us to the content. We'll delete it as soon as we see the flag. (You can of course also delete it yourself. If you do, please flag it anyway, so that we are aware of it. In this case it is crucial you fill in the edit summary with something like: Removed link to illegal content.)


• Both free and commercial resources are allowed, but make sure to include a note if they are the latter. Remember the rules about self-promotion. Include also if registration is required.


• Include links to the sites only, don't post images, they would take too much space.


• Add the resources in alphabetical order so they're easier to find.


• For the resources, a short summary is very much appreciated.

If you have questions about these guidelines, please head to meta to make yourself heard. The above points are not set in stone and might change in the future.

Alphabetical Index

Currently those are all categories. If you think, that a new one should be added, please submit an answer in the corresponding meta thread. (A comment is probably not sufficient, as it does "bump" the question on the active tab.