Resource Packs
Pack previews, faster pack switching, hiding packs made for other versions, and tweaking a pack without editing it.
Sour replaces the resource pack screen with its own. It opens from Options as usual, and on a server the Esc menu shows Resource Packs where Open to LAN would be.
Previews
Hover a pack and a card shows what it actually changes: swords, blocks, hearts and more. Pick which items appear under Pack Preview Items in Settings, and how big with Preview Size. Turn the card off with Resource Pack Previews.
Faster switching
Fast Pack Switching skips work a pack swap cannot change, such as restarting the sound engine when neither pack has sounds. It is on by default.
Packs for other versions
Show Pack Version labels which Minecraft version a pack was made for. Hide Incompatible Packs leaves packs for other versions out of the list; packs you already use stay.
Changing a pack without editing it
Pack Tweaker gives you borderless glass and recolours wool, clay, glass, leaves, stone or clouds on top of any pack. Low Fire lowers the fire overlay. Pack Display shows your current pack on the HUD.