6 PowerPoint productivity boosters from BrightSlide | BrightCarbon
The free BrightSlide tool from BrightCarbon offers a number of useful features for working in PowerPoint
Free Powerpoint templates and Google Slides themes for presentations - SlidesCarnival
Templates for PowerPoint for Google Slides. A good place for inspiration even if you aren't going to use the actual templates.
Simulation Tools for Every Budget
Tools for branching scenarios, from free and simple to expensive and complex. PDF, PowerPoint, BranchTrack, Inklewriter, Twine, Storyline, and SimWriter.
Cometdocs
Online tool for converting PDF files to Word, Excel, PPT, etc. It does a good job of making text editable, but converts SmartArt as static graphics. It would work for small text edits in a presentation where you don't have the original PPT file, but if you had a lot of SmartArt to rebuild it wouldn't save much time. It might work better for Excel spreadsheets than the PPT I tested.