Hello,
I (re)discovered n8n very recently and spent a couple of days creating automations but I've run up against what appears to be a bug that makes it difficult to perform flow control. I would like to ask if Node-RED is a suitable replacement.
A feature n8n is missing is the ability to see if a workflow is already running and stop other workflows. Can this be done with Node-RED? I tried to work around it in n8n by creating a semaphore system but the bug in n8n stops it working correctly. If Node-RED requires a workaround too, has anyone already made one?
node-red is very flexible with everything, but it may require additional work.
If your request is truly binary: only 1 flow may run at the same time, then it can be quite simple, by using flow context variables that can be set within a flow
eg.
Other flows can check this variable.
There is also a node for flow control/semaphores
It all depends on your needs. It is rare to see a problem that couldn't be solved in node-red 
have fun.
Craig has rightly mentioned using a context variable. But it is also worth mentioning the rich community of nodes. There are certainly gate nodes that make this a very easy thing to control.
But also worth noting that Node-RED really only runs a single "Flow". Under the skin, all tabs and flows (small "f") are all part of the same Flow.
Also, most of us prefer to use event-driven flows rather than gated ones. So a flow (small f) is not receiving any messages until an event happens. Obviously, this is not always possible but is the preferred and more robust design pattern.
