UPDATE: March 2017: Assembla has a new management team, and has significantly changed their model. When I wrote my original review, Assembla was reasonably priced for small teams or occasional users. That is not the case anymore. Their cheapest option is $75 per month, which drives the occasional user totally out of the market. I am no longer an Assembla customer.
I have only been using Assembla for a couple of months, but it has been a breath of fresh air compared to the tools I was previously using.
There are two ways you can use Assembla, and I'll try to point out the differences here, because I think they are very important to new users. First, you can use Assembla as a free tool for cloud-hosted source control. You can have an unlimited number of GIT, Perforce, or SVN repositories, grouped into an unlimited number of "Spaces" with an unlimited number of named users that have access to a specific "Space." The limit here is that you can only host up to 500 MB of content combined across all your spaces and projects.
The second way, is to use Assembla as a paid tool for product management. This option includes some great project management tools, as well as some of the features of cloud-hosted source control, but has some strange limitations. For example, if you are a paying customer, you now have a limit to the number of spaces and users that you can connect to your system. Free users have unlimited spaces and users, but paid users have a limit, based on how much they pay. Granted, the storage space is larger for paid users, but the limits on paid users and spaces is bizarre, when you provide unlimited options to your non-paying customers.
As a cloud source control repository, Assembla is awesome. I love it. It is easy to set up, easy to manage, easy to connect to, and easy for my clients and co-workers to use.
As a paid member, the project management tools are excellent. The card wall is easy to use and easy for people to understand. The ability to link to specific tickets when you commit from source control is amazing, and one of my very favorite features of Assembla.
I hate (and I mean that in the nicest way), but I HATE that as a paid subscriber I have fewer options available to me for spaces and users than your free customers do. That just boggles my mind. I want to recommend Assembla to people in my field (as I'm a consultant in my industry), but I can't get over how you limit your paying customers in ways that you don't limit your fee users.
UPDATE March 2017: Assembla resolved this concern by removing free accounts and raising the prices on paid accounts (from what I can tell). I can't find any options on their website anymore for free accounts.
You may need two accounts: one free account for working with SVN repositories only (so you can have an unlimited number of spaces), and one paid account for working with project management tools. I wish I didn't have to recommend this, but Assembla's insane policy on providing paying members with fewer features (specifically in number of spaces and users) makes this the option I've had to resort to.
As a consultant, I'm working with several different companies at the same time, trying to keep all my projects up to date, and managing communication with my clients. Assembla makes it easy for everybody to stay connected, to understand the current status of the project, and to contribute in meaningful, easy ways.