Beyond the Scanlines - a YouTube channel covering retro games, often looking at some oddball stuff that wouldn't normall get coverage. Well thought out, and very well presented
Game Development Tools
AESprite - not sure this needs any introductions, but it's a great modern graphics editor for doing sprite work
LDtk - a free and open source level editor with some pretty powerful features
Retro PC Software
Plop Boot Manager - a boot manager that looks cool but also supports a huge list of features
TestDisk - a tool for restoring and fixing lost partitions. This would have saved me multiple times 20+ years ago. If you've messed up a partition table this will help you restore it in next to no time