MultiBit is one of the unsung heroes of the bitcoin world. The desktop bitcoin wallet software, launched three years ago, recently surpassed 1.5 million downloads and, in fact, Gary Rowe, one of two core developers on the project, puts the estimate at more like 1.8 million this month.

Now he and development partner Jim Burton are about to start charging tiny fees for using it.

One of the things that must have helped MultiBit a lot was being listed on bitcoin.org. The wallet is one of five desktop wallets listed on that site, and is outpacing at least some of them.

CoinDesk reached out to the bitcoin core development team to ask how many people have downloaded BitcoinQT, the reference implementation of the bitcoin client, but received no response. Electrum, one of the other five wallets, also failed to respond.

What we do know is that Blockchain, the downloadable mobile wallet that also has an online counterpart, has just over 1.6 million users. This chart shows the market increase in downloads since December, after the price of bitcoin spiked.

Coinbase

's online wallet has also garnered 1.2 million users as of April, according to data from the company and isn’t the only wallet to see a recent jump in downloads.

Another veteran wallet, Armory, has had about 200,000 downloads in total since its first alpha release in early 2012, according to its core developer, Alan Reiner. The download rate has increased substantially of late, with half of that figure coming in the last six months, giving around 17,000 downloads each month on average since November.

“We get 70-85% of our downloads from bitcoin.org, by being featured on the ‘Choose your wallet’ page,” said Reiner.

Mac-based wallet Hive is doing very well, with 125,000 downloads thus far (most of which come from this site, according to the founder, Wendell Davis).

While Hive came out of beta in February, it was first launched for download in November. At that rate, it received around 21,000 downloads per month on average since its beta launch – around 40% of Multibit’s average, if we also average MultiBit download numbers over its entire existence.

"We expect mobile numbers to eclipse fairly quickly once we get rolling," said Davis, whose firm bought Android app Bridgewalker last November.

However, with 1.8 million downloads to date, the MultiBit project could be described as a victim of its own success. The more users that download a project, the more support calls start coming in.

“Back in October and November, we were getting 20,000 downloads a day, when the price was going bananas,” Rowe said. “What we found there was that lots of people were asking us questions, but it was the same thing, over and over again.”

The duo updated the website with support articles that had previously languished within the issues database. It also includes a basic HTML browser in the product itself, so that they can serve up help files.

“We had to introduce a few little hurdles that people would go through. If we introduced a 'help' email at the top of the support page, we’d be inundated,” he says. Those hurdles include setting up github accounts.

Then, there’s the occasional bug that blows up. That happened last month, when a firestorm erupted on reddit, after a user alleged that the firm’s wallet had eaten one of his private keys, depriving him of his coins.

That user – who has since stopped answering messages from CoinDesk, and hasn’t appeared on reddit since – caused a flurry of criticism on other boards, with users accusing the developers of scamming users.

The answer to that technical problem on the forum, from Burton, where he talked about problems getting his lights working seemed to inflame users even more. The post showed an underlying frustration common to developers on any free software project: they are resource-constrained.

Eventually, the two developers just threw out the code responsible for that complaint, rather than trying to fix it. Mike Hearn, the developer of bitcoinj, the software library underpinning MultiBit, came on board to help and the team removed a feature that enabled users to import private key data from Blockchain.

“We just thought it’s better that we take it out entirely even though it is possible to fix it, because that introduces more stability, because there are fewer things to go wrong,” said Rowe, who added that, because of this issue, the pair lost around two weeks of development time on the next version of the wallet.

Hopefully, cases of lost private keys won’t occur when that next version appears. The software will use Hierarchical Deterministic (HD) technology, meaning the wallet uses a data structure that lets you produce large numbers of private keys from a tree of data.

The whole tree can be encoded in human readable form, simply by entering a passphrase. That tree, along with all of its addresses, can later be reproduced with the words, even without connecting to the Internet.

“Let’s say that disaster strikes and your laptop drops in a canal,” said Rowe. “So, you reach into the firesafe, pull out the paper, download MultiBit onto your new laptop, type in the 12 words, and off you go.”

The company will also include strong encryption technology into the HD version of the MultiBit wallet, enabling users to back it up to the cloud if they want to.

Other features in the pipeline include integration with the recently introduced bitcoin payment protocol, which has already been adopted by BitPay and Coinbase. And MultiBit is working with the creators of the Trezor hardware wallet to integrate with them too. This would put secure signing capabilities in a piece of hardware.

“At present bitcoinj isn’t 100% Trezor compatible,” Rowe said. “To get it fully integrated will take a bit of time.”

Time is the problem. Redditors may grumble occasionally about problems with the wallet, but the issue is that these two are working on the project almost single-handedly.

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Rowe has a day job doing IT contract work, and while he has been able to take several months off to work on MultiBit, he has to spend some of the summer back in normal contract development, meaning that his work will be restricted to evenings and weekends.

Jim Burton, the other developer working full-time on the project, will also have a hiatus this summer.

Part of the problem is that there aren’t many people working on the wallet. The github page shows just eight contributors. And that's by design.

“Never before have we had an open-source library that anyone can download, that enables anyone to send money anywhere in the world,” Rowe explained. “That has to be protected.”

Hence the team is very conservative about giving anyone commit access.

This approach causes a bottleneck, though. MultiBit has been taking donations, but has received around 50 bitcoins since the start of 2012. That’s 1.8 bitcoins a month. Enough to keep Rowe and Burton in pizza and beer for coding sessions, certainly, but hardly a coder’s salary.

They’ve been hoping for a large donor to come along and drop $200,000 in their lap, but as this doesn’t seem likely, they’ve decided to take another approach, which they’re calling the Burton-Rowe Income Technique (BRIT).

The wallet will in future charge 1,000 satoshis per spend. That’s about half a cent at today’s price. Put another way, said Rowe, 800 bitcoin transactions made through MultiBit will earn the developers a latte.

If MultiBit becomes popular, and they get excess funds from the charges, the grand plan is to push some of that money on to other code libraries on which it relies. What isn’t yet clear is what would constitute an excess, or how that money would be allocated.

Will users baulk at the idea? Rowe said he hopes not.

“That’s such a speck of dust that the vast majority won’t even notice it,” he said. Indeed, this is below the official dust threshold, meaning that the wallet has to wait for a user to make several transactions before it can bundle them up and send the developers an amount. "But to us, because we’re able to aggregate that tiny fee, that gives us enough money to sustain development.”

So, MultiBit will charge 0.5 cents per transaction at today's prices. It would seem harsh for users to complain. After all, they’re getting a free, long-established wallet, created by two developers, for the love of the project. It’s an interesting experiment. The question is, will you download it?

Wallet image via Shutterstock