Can anyone recommend an alternative to Visio for doing Mechanical FBD's that is free online?
Use DraftSight. You can download, install and use; all for free
LibreOffice Draw does good flow charts as well, and you get a full-featured Office package thrown in :-)
Some of the best visio alternatives are Lucidchart, Smartdraw, Dia, etc... Lucidchart is the most popular one with lots of templates and uses.
Source: Top 10 Best Microsoft Visio Alternatives 2020 | My Chart Guide
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