Very simply, Simple DirectMedia Layer, or SDL for short, is a library that allows you low level access to a video framebuffer, audio output, mouse, keyboard, and joysticks across a wide variety of operating systems.
The current version supports Windows, macOS, Linux, iOS, and Android. SDL includes code for many other operating systems but they are not officially supported. See the page about Installation for the most recent list.
The latest stable version is SDL3. You can always get the very latest bleeding edge Git snapshot, which may be broken at any given time, from the GitHub project page.
You can send questions and feedback through the SDL forums/mailing list or using the Feedback link (at the bottom of any wiki page).
You can submit bug reports to SDL's GitHub issue tracker and, if you like, send patches as GitHub pull requests.
We run a Discourse server here, which can be put in "Mailing List Mode," where you create an account on the website, flip a switch in the preferences, and then can interact exclusively through email thereafter.
Yes, you can find people hanging out on the IRC server at irc.libera.chat on the channel #SDL
Yes, go here!
Yes, the official SDL logo was created by Arne Claus, and is available here.
Yes, you can click the "offline html" link at the bottom of any wiki page to get a zipfile archive of the entire wiki in HTML format. If you like Unix manpages, we generate manpages from each API function's wiki page. The latest archives for each supported project, as zipfiles, are always here.