Will Spanbox slow my computer down or eat RAM like running five separate Electron apps?

It's generally lighter than running five separate desktop apps, but I won't oversell it. Each of those standalone apps (Slack, Discord, WhatsApp desktop) ships its own full browser engine, so five of them means five engines. Spanbox loads your apps as web sessions inside one shared shell, so there's less duplicated overhead and a lot less taskbar clutter. It won't conjure RAM out of nowhere, more connected apps still use more memory, but one window running several is usually easier on the machine than a pile of separate Electron apps, and you can close the ones you're not using.

Noticeably better than five native apps for me. The standalone versions each haul their own Chromium; Spanbox shares one, so it's less heavy and my fans stopped screaming. Not zero, but better.