Hosting Open Source as SaaS

I would be surprised if serving ads would pay for the hosting/bandwidth/tech support required to host some of the open source SaaS applications. This would provide huge experience at low risk, and absorb significant hours.

MantisBT is a free popular web-based bugtracking system that might fit the model.

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20081117
Teamwork is a Web-based groupware for project management. It supplies groupware, issue tracking, cost control, and document and project management features with fine-grained security in a friendly interface.

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200812
Team tasks does project management. There are others.

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20090331
Request Tracker is an enterprise-grade ticketing system which enables a group of people to intelligently and efficiently manage tasks, issues, and requests submitted by a community of users.

RT Hosting Plans
Gossamer offers four different hosting plans for RT. If you are unsure of what would be the best fit for you, please contact them with the details on how you plan to use RT.

Bronze - $125 a month
For companies processing up to 500 tickets per month
Shared Server - Dual AMD Opteron Server, 4 GB of RAM, 73 GB RAID 1 Drives, 64 bit Linux

Silver - $350 a month
For companies processing up to 1000 tickets per month
Dedicated Server - Single AMD Opteron Server, 1 GB RAM, 40 GB Drives

Gold - $800 a month
For companies processing up to 5000 tickets per month
Dedicated Server - Dual AMD Opteron Server, 4 GB of RAM, 73 GB RAID 1 Drives, 64 bit Linux

Platinum - $3250 a month
Unlimited tickets per month
Custom Cluster - please contact Gossamer for more information

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201101
Heroku. Ruby cloud platform as a service.