The Intangible Assassin
The Intangible Assassin project is a series of spells based around effects like Opening the Intangible Tunnel (ArM5, page 162). The main purpose of the effects is for the magus to be effective at waging Wizard's War, although of course, this is not the only strategy for excelling at Wizard's War. Many of the components in this project are also useful for gathering information about and attacking opponents other than magi.
A lot of the effects in this project are low level, as one of the challenges encountered in Wizard's War is Penetrating the Magic Resistance of your opponent. Note that this means that although many of the effects might be easily cast spontaneously, it is still worthwhile for a magus to invent the formulaic spells — Penetration is the key to using these spells.
The components of this project can be easily invented by a single magus acting alone, or by a group of magi working together. Of course, magi who work together on this project must trust each other a lot. Naturally, it is not compulsory for a magus to invent all of the effects in this project.