Product Roadmap Tools
A product roadmap is a strategic document that aligns multiple teams in order to bring the product closer to the vision. A product roadmap is not a project plan, but instead a flexible path to building the ultimate product. Product roadmap tools allow you to visualise your roadmap and do multiple other things such as capture feedback, vote on features, prioritise and more.
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Google Slides
Sometimes the simplest solutions are the most elegant. Google Slides is a powerful collaborative slideshow creation tool and works well for creating and collaborating on product roadmaps.

Aha!
Aha describes itself as "The world's #1 roadmap software", while we can't certify the #1 rating their product is quite packed with features that allow you to priortise ideas and also integrate into development management tools like JIRA. Aha is definitely one of the most polished dedicated tools for roadmapping.

Roadmunk
Roadmunk is another dedicated roadmapping tool similar to Aha. The feature set is quite comparable and is the more affordable option compared to Aha. Based on reviews it looks like Aha wins in overall UX.

ProductPlan
ProductPlan supports a depth of integrations including Trello, Slack and Microsoft teams. Based on user reviews, it looks like ProductPlan has an easier learning curve and is quick to get up and running with.

ProductBoard
Productboard says that they "help product managers understand what customers need, prioritize what to build next, and rally everyone around the roadmap.". ProductBoard differentiates itself by focusing on integrations with various customer insight tools such as Intercom, Zendesk, Gainsight etc.

Google Sheets
If you don't care about visuals, then a spreadsheet may be all you need. With advanced scripting you can also do neat things like highlight product features that may have already shipped and ones that are coming up.