Twimbow, a Web application that helps social network users organize and communicate with their friends with lots of pretty colors, is calling it a day. The startup says it is “disheartened” by Twitter’s recent outlining of new API rules.

When those new ‘Rules of the Road’ were first announced, it was clear that they were bound to affect a number of companies building tools and services on top of Twitter’s API. It did quite some damage to Twitter’s reputation among third-party app developers, and Twimbow’s abrupt ending won’t be doing any good either.

It also doesn’t help, of course, that chief executive officer Luca Filigheddu recently left Twimbow to focus on a new job at Research in Motion as BlackBerry Developer Evangelist for the Italian market. For the record: he was still on Twimbow’s board.

The Twimbow team writes:

today is a sad day here in Twimbowland,

In the last communiques, Twitter discouraged the development of new applications replicating the core Twitter Experience, called “Traditional Clients”, among which Twimbow is included.

They outlined some rules which disheartened us and now we have no longer enthusiasm to continue our adventure.

About the new rules, deemed ‘too binding':

All those that earlier were just Twitter’s “ best practices” about their data visualization, have become rules too binding for us. We want to create innovative products, no one can force us not to stun our client or to visualize data not our own way.

We made huge efforts to launch our mobile app for all the platforms out there, but, reluctantly, we cancelled those projects.

Twimbow will no longer be developed further, although it will remain available until Twitter goes live with the new API (which is expected to happen within the next 6 months).

I had a quick chat with Filigheddu on Skype today, and he told me that the main problem is that Twitter will impose a cap of 100,000 user tokens in v1.1 of the API, without exceptions. Twimbow tried to find a work-around to keep its service running viably, but Filigheddu says there was simply no way.

That’s notable, because Twitter explicitly said it would only be making life difficult for a “small set of clients” that basically replicate the ‘core Twitter experience’.

It’s not that Twimbow was one of the most popular clients in the ecosystem, but it was a nice little, colorful third-party Web app that had something of a cult following.

Screwing them over simply doesn’t make Twitter look good, either way you look at the situation.

Coincidentally, Twitter chat service Bonfire also announced that it will soon be shutting down this morning.

Bonfire and Twimbow are not the first to leave the Twitter app scene, and they evidently won’t be the last either.

Any guesses who will be next in line to turn the page?

Also read: Twitter kills off @Anywhere