ImprovMX has always worked great. I have used it for a handful of email addresses that all forward to my personal account. If your personal account is gmail it's also very easy to set up a "send as." I will definitely use this first next time I need something like this.

ForwardEmail is indeed open source and works pretty good. It's a little more setup than ImprovMX and I did have an issue where sometimes mail would bounce back to the sender and they would tell me about it. I don't know whose fault it was tho, because it was only one sender and her SMTP server was strict. I did also have an issue where all the mail was going into the spam folder of my personal email, but I'm pretty sure it was my fault. I clicked "spam" for a spam message and then gmail started assuming everything from forwardemail.net must be spam so silently "helped" me by hiding everything D-: Once I figured it out I was able to fix it by marking the emails as "not spam" but it occasionally would spam something I needed. So, if you use either of these services, never mark the message as spam. Also if you use forwardemail throw the dev a few bucks (https://forwardemail.net/en/donate) . Here's the code: https://github.com/forwardemail/free-email-forwarding