Irdest is a decentralised networking project, aiming to create easy-to-use solutions for ad-hoc wireless, and mesh networks. It supports many common desktop operating systems (Linux, Windows, MacOS, NetBSD, …), and Android mobile phones. iOS support is on the roadmap.

"not sure who needs to hear this, but you can be excited about community self-determination and decentralized infrastructure.. without blockchains." / Twitter

MrBotchi is federated microblogging platform for single-user.

Grid layout, pinned contents, works for microblogging as well as blog posts & images posts.. maybe the closest thing to a decentralised Tumblr so far?

A local-first collaborative corkboard app. Designed to collect all the information you need and synchronize it across all your computers. PushPin supports taking notes, and can archive web content, images, PDFs, audio, video, and any other files you might want to hang out. It can synchronize across all your devices, and doesn't require any infrastructure to operate.