I think you want to have something that I already used recently in my previous company “Redmine” and solution was delivering everything you need, it’s standalone project tracking system easily deployed with Ubuntu LAMP Stack or Windows, MacOSX(We used it on xUbuntu desktop HP DC 7500 Core2Duo machine with 4gb ram). My experience suggests you replace Cinamon with 16.04 xUbuntu which uses XFCE environment and is much lighter and friendly with older configurations and laptops, tested with many different configurations and was always on point, no crushes, programmable as you want it, if you know to administrate and set-up machine for LAN or LAN + remote login from outside after you secure your server.
You can see what it offers here and go download, install, set-up and play around with your team to see if it does what you want.
Redmine is a flexible project management web application. Written using the Ruby on Rails framework, it is cross-platform and cross-database.
Redmine is open source and released under the terms of the GNU General Public License v2 (GPL).
Some of the main features of Redmine are:
Multiple projects support
Flexible role based access control
Flexible issue tracking system
Gantt chart and calendar
News, documents & files management
Feeds & email notifications
Per project wiki
Per project forums
Custom fields for issues, time-entries, projects and users
SCM integration (SVN, CVS, Git, Mercurial, Bazaar and Darcs)
Issue creation via email
Multiple LDAP authentication support
User self-registration support
Multiple databases support
Third-party Redmine bundles
TurnKey Redmine Appliance - Provides a free lightweight Debian-based Redmine appliance (available as an ISO, virtual machine image or cloud image).
BitNami Redmine Stack - Provides an all-in-one installer and free virtual machines and cloud images for Redmine.
Pick your poison, its done in 5-10mins. for your LAN set-up environment usage and ready to go, you all register over HP DV6000 set-up as server machine and that’s it, no headaches.
edit: just want to point out that everything is kept in DB on your HP DV6000, nothing goes out of your LAN and nobody comes from outside of your LAN set-up. Classic usage is, you make new project, select people who work on it, give them tasks, deadlines, everybody pull, push and commit just like on Github or any other Git solution but in your LAN and on DV6000, Enjoy