is it possible to change from redevent to JEM?

You're welcome to use JEM.
The question is: Do you need old or archived events you posted in the old extension? Normally no!
If yes (because they are actual), you have to find a way to export this and to bring it into a csv which is compatible to the JEM. To find how is build JEM csv file, you can export a JEM file and analyse it.
Because it seems redevent doesn't continue, it doesn't need a plugin!

Hi Jojo,
thank you for the immediate answer !

Youre absolutely right - if they stop, no sense in programming a plugin, maybe only for my migration time...

I have a lot of People coming from Google for elapsed events, I have to take care for that. And we are giving seminars which repeat every year, so I have to recycle events often.

Markus