I seek free software for Windows 10 OS, with the following features for IE and Chrome and Firefox:
automatically completing forms and fields;
I can't use Roboform anymore, as it's expensive. What alternatives are there?
for security reasons i would strongly advise against web-based services to store your secret passwords!
instead i would highly recommend a local installed open source software and just sync your encrypted passwords across your devices via any sync-service...
With its countless ports (even for Android, iOS, Windows Mobile, BlackBerry, etc.) you are platform independent and don't have to hand over your passwords to a cloud service.
I know you might be hesitant to sync your passwords and form fills with a cloud service, but if it helps you feel better if the service is open-source and constantly being updated, I would check out Bitwarden. It's free unless you want a little storage space for important files along with its other capabilities, and if you decide you want that, it's only $10/year. You can learn more at http://bitwarden.com/. Also, LastPass (http://lastpass.com/) has a really good free plan. That's what I use since Bitwarden didn't have some of the cool features LastPass has.
Enpass is free for all desktop OS though its mobile (Android/iOS) versions are freemium.