The (Basic flowcharts or advanced technical blueprints?)
Excellent for visual brainstorming, mind mapping, and agile workflows. Official Microsoft Solutions
A free, open-source desktop application that includes native tools for vector graphics and flowcharts. How to Stay Safe Online
Using school computer labs without installing software.
Modern antivirus software does not catch everything. Many portable repacks use obfuscation or are FUD (Fully UnDetectable) at the time of download. By the time antivirus definitions catch up, your machine could already be compromised.
I can recommend the exact software that matches your workflow. Share public link
Do you need to , or are you starting from scratch?
Leaves no leftover files on the host computer system.
Microsoft ended all support for Office 2007 and Visio 2007 in October 2017. Critical Risks of Using Unauthorized Portable Apps
Completely free, runs in your browser, and offers a legitimate portable desktop app.