Small towns with:
Check out Bonn. Siebengebirge just around the corner is beautiful, Bonn is progressive with a good mix of nationalities (DPDHL, Telekom and NGOs means many Expats), smaller and less hectic than Berlin, more affordable than Munich and better weather than Hamburg.
Drawbacks include rising cost of living and the next startup community (small but growing) being in Cologne (30min by train).
Lauterbrunnen, Switzerland, hits your first three (fails miserably on the affordable requirement, but is great if you have the money).
Ljubljana, Slovenia might be a good bet. I don’t know about the startup culture, but there’s at least one cool co-working space and it’s definitely affordable, close to nature (30 minutes by train and you’re in some of the prettiest landscapes in Europe).
I’ve never been there, but if all the tales are true, Estonia seems like a great place to be a digital nomad and/or tech entrepreneur.
I’m actually thinking of moving a holding company there.
Can anyone can verify the lifestyle at Estonia?
Freiburg Im Breisgau Germany. http://www.freiburg.de
I’d love to be in this area, it’s in the so called blue banana zone. https://en.m.wikipedia.org/wiki/Blue_Banana
How about 4 out of 5? Good enough? If 2 (progressive) is not crucially important, I suggest checking out Lisbon.
@twaldorf is from Boulder and has visited few places in Europe, maybe he can give some mindful answer.
Yeah I think Lisbon ranks high despite not being very progressive. I think it’s still a little too big and messy for me, I really wanted something smaller.
I can second Freiburg. It’s one of my favorite places. I used to live there for three years and this summer returned to do some nomading. Can even suggest some cafés to work from. In Summer you should absolutely hang out at Jos Fritz Café. They have a quiet shady beergarden with free wifi, and nobody cares if you don’t order something for hours.
But I’d have to add that it’s not a great place for IT/nomading if you care to meet other people with similar interests. Apart from the small IT faculty, there is barely any IT industry to talk of. People generally are a little anti-computer and all about being outdoorsy, political and sustainable. Don’t expect them to be super excited when you tell them what you do 
Maybe some people will even scowl.
Nonetheless, the vibes are awesome there and I’m sure they will broaden your horizon when you get to know them. Moving there was one of my best decisions so far.
Cambridge in the UK is the closest town to Boulder that I’ve seen thus far, but it fails rather miserably when it comes to outdoor adventure opportunities. Other than that, all boxes checked–good startups, progressive + smart community built around a university, laid back, and about as affordable as Boulder or Portland (which is to say not very unless you live in a nearby village. Again, just like Boulder or Portland). It even has a large metropolis 40m away.
Grenoble ?
Geneva ? (ok not affordable )
Maybe Lyon, Nice (expensive), Montpellier ?…
Sounds like Brighton, UK.
http://www.theguardian.com/technology/2014/jan/12/brighton-leading-tech-startups
http://www.nationaltrail.co.uk/south-downs-way
http://northlaine.co.uk/
The vibe in Brighton seems definitely more laid back than in London. I liked it when I visited for a couple of days. Although I gotta say, the outdoors in England are quite repetitive and the sea is not very enjoyable. It’s more personal than anything else, after 5 years of UK I’d rather go somewhere else!
From what I’ve read so far, it seems that most laid back and progressive locations with some startup community can be found in the north side of Europe, which is a shame as the south is so beautiful and much warmer. I have a strong connection with the mediterranean sea and I feel happy just by smelling the vegetations and seeing the warm colours. It would be jackpot if I could find a Boulder near the mediterranean sea, or even within 100-200k range.
Anything in Southern Europe that matches my criteria above? Even if 4 out of 5
Agree with @gianluca_trombetta - would be nice to find somewhere hotter! Currently living in Brighton and although we have an ace kite surf and water sport scene, it’s not quite the med.
I’ve been looking at Tarifa and Lisbon as next possible locations…
I definitely recommend Brighton, it’s got a great alternative scene, lots of decent beer and burger joints, and very closer to the south downs.
The weather probably matches Portland closely, it’s pretty miserable in the winter but the summer is glorious.
I wouldn’t say the tech scene is thriving but better than average.
If you where considering Berlin, you might want to look into Leipzig. It’s not too far from Berlin (about 1-2 hours south) and has a similar vibe, but is smaller and more affordable. Climate will be roughly the same of course. But lots of lakes around, very bike friendly and very good kayaking in and around the city. No mountains though…
Aosta is pretty close to Boulder. Less prestigious university and slightly light on on the start-up scene but growing.