Since completing his term as New York City’s mayor last December, Michael Bloomberg has turned his attention to the vexed question of how to smarten up cities across the pond.

Bloomberg Philanthropies’ Mayors Challenge (not, sadly, a kind of mayor beauty pageant) invited European city governments to propose solutions to “major urban challenges”; last week, Bloomberg handed out a total of $11m to the five winners. The top prize went to Barcelona, which took home $6.5m. The other four received $1.3m a piece.

Here’s a rundown of the chosen projects:

1.Barcelona’s Facebook for the elderly

Barcelona’s catchily named “Collaborative Care Networks for Better Aging” proposal  will create a “digital network” (carers, friends, family member, social workers) around each elderly person in the city. In this way, it’ll “identify gaps in care” and “promote quality of life”.

One in five of Barcelona’s 1.6m residents is over 65 – a proportion which is pegged to rise to one in four by 2040 – so the platform could end up being one of the city’s most-used social networks.

2. Sweden’s climate change-battling charcoal

Stockholm’s proposal centres on biochar, a form of charcoal produced from organic waste, which can be used as a fertiliser or to filter water (though not, one assumes, at the same time).

Residents will bring organic waste to collection centres, where it will be converted into biochar then redistributed. The substance “sequesters” carbon – trapping it in the soil, rather than in the atmosphere – so creating it can help tackle climate change.

3. Sharing in Kirklees 

The smallest city to receive the award is the metropolitan district of Kirklees, West Yorkshire (essentially, Greater Huddersfield), which will use its money to promote the sharing of under-used local resources.

Vehicles, venues, and citizens’ skills will be listed on an online platform, where users can get in contact to borrow, swap and barter. Kind of like Gumtree, but not-for-profit.

4. Beacons for the blind in Warsaw

Warsaw’s plan is to install thousands of “beacons” around the city that would interact with users’ mobile phones. This’ll allow blind people to navigate more quickly and easily through the city.

5. A “save our city” forum in Athens

According to the Mayors Challenge website, Athens hopes to launch Synathina, an “online platform that will connect the new dynamic input of civil society with local institutions and local government to collaboratively devise solutions to local problems”.

Haven’t the foggiest, to be honest.

Our best guess is an online forum where Athenians discuss how to tackle the problems the city’s facing post-economic crisis. Worth a try.