First of all, it's sad to see some of the folks here suggest using wine or a virtual machine. Not only is it an inappropriate answer to the question, but also, in my humble opinion, it is against the spirit of the Ubuntu community to use and promote proprietary Windows software.
But back to your question, Proteus has two famous products Proteus PCB, which is an EDA suite (electronic design automation) and Proteus VSM for analog circuits and microcontroller (MCU) simulation. You did not mention which one you are referring to. Still, people usually look for VSM alternatives as it is a great software for simulating MCUs and the Arduino AVR development board. Unfortunately, there are not many cross-platform free, liquid, and open-source software (FLOSS) as powerful and feature-rich as Proteus VSM, but there are some attempts. I will try to list them here:
- KTechLab
- SimulIDE
- BrainBox
- PICsimLab or PICsim
- PIC-Simulator
- simavr
- SimulAVR and simulavr-disp
- SPICE (Simulation Program with Integrated Circuit Emphasis)
- QUCS (Quite Universal Circuit Simulator), Qucs-S, Qucsstudio, Qucsator
- Ngspice, Spice3f5, Cider1b1, and Xspice
- Xyce
- Circuit Simulator or CircuitJS1
P.S. I have created a curated list of all FLOSS electrical engineering software here.
wineHQ
for installing windows software ortryton-proteus
binary package in Ubuntu Oneiric amd64