Purposely plan regular 1:1 breakfast or lunch meetings with a long list of assorted friends/colleagues. Engage in the lost art of live conversation. It takes effort and forethought, people can get busy. That makes it all the more important.

Find a cafe or coworking space. You're in Nantes, right? Check out the Nantes Cité des Congrès and Nantes Route de Paris, they both have dedicated coworking spaces. Personally I would find something right on La Loire or L'Erdre so I had a nice view of the water; really any view of nature I think will help, even if nobody's around. After work, get out and find something to do with other people.

Company wide IRC type chat with several non-business chat channels to socialise in (eg. Tech, Food, Fun, Sport). Can use an IRC server, jabber/XMPP or Hipchat for this.

Plus regular real world trips to meet/connect with the people you work with, and an active social life outside work.

It of course helps if you're the kind of person that likes solitude.

I may be an outlier; it takes me about two weeks of not interacting with another person to feel the least bit lonely.

Our IRC chat (flowdock) has a section which is basically water cooler discussion and copious amounts of gifs. Normal work takes place in other channels.

Other than that...

rdio subscription

Local meetups

"bring my dog to work" self-made perk :) He hangs out in the same room I'm in for most of the day.

I've been telecommuting since 2000 and definitely pets help. I have two cats and a dog.

Sometimes I work at the library or cafés. Meetups are great too.

Volunteer work outside the house once in awhile.

First I smiled but then I thought that, indeed, a pet is quite possibly a good idea if the rest of the family and your life can accomodate it

Unless you have a family, try working in coffee shops and coworking spaces more than you work at home.

And really unwind with your friends on the weekends, to the point where you wouldn’t mind not seeing another human being the Monday after.

Have short meetings with your team every day. Make jokes and share fun things. Implement a Social Network for your company/team. Join a shared office space or go to a cafe where people are working like you. Exercise every day. Meet with face to face with friends in the evenings.

There is always the option of traveling abroad always staying in places with good internet connection. You get to meet new people all the time: http://locationindependent.com/

We use Sqwiggle (https://www.sqwiggle.com/) which is almost like being in the office - everyone's there when you need them.

Would totally agree with caw about getting a dog though!

Join a shared office space. It's difficult, spend more time around family.