#murally

Mural.ly - a digital whiteboard of all your ideas

BMFiddle - a concise business model canvas

Blossom - a beautiful project management software for agile thinkers

Validation Board - a must-have when going through idea revisions

Typeform - a great survey tool for your problem and solution interviews; use when surveying over email, include links to your demo

Moqups or Invision (for the design-skilled) - a cheap and fast way to build a first demo of your product

GanttPlanner - a helpful tool to turn your Google Calendar into a Gantt chart

By the way, Blossom integrates with Slack, and so do many other tools, when using Zapier.